Software Alternatives, Accelerators & Startups

Sideline VS ForthWrite

Compare Sideline VS ForthWrite and see what are their differences

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Sideline logo Sideline

Sidelineโ„ข is the free 2nd number for your smartphone. It uses your existing carrier network so your 2nd number works anywhere your cell phone does.

ForthWrite logo ForthWrite

Email that sounds like you, and gets measurably more like you every week. Drafts in Gmail, Outlook, and the browser. Free to start.
Visit Website
  • Sideline Landing page
    Landing page //
    2023-07-07
  • ForthWrite Landing Page
    Landing Page //
    2026-06-19
  • ForthWrite Dashboard
    Dashboard //
    2026-06-19
  • ForthWrite In Gmail
    In Gmail //
    2026-06-19
  • ForthWrite Pricing
    Pricing //
    2026-06-19

ForthWrite is an AI email writing assistant for Gmail and Outlook that learns your writing style from your real sent mail. The more you use it, the more it sounds like you. Get smart drafts in seconds, auto-draft replies before you open your inbox, and maintain your personal voice at scale. Free to start, no credit card required. Works inside Gmail and Outlook on the web.

How it works

ForthWrite captures your tone, sentence rhythm, and sign-offs from your actual sent emails, then uses that profile to generate drafts that match how you write, not a generic AI voice. Every draft you edit or send improves the model over time.

Key features

  • Auto-draft: replies waiting in Gmail before you open your inbox
  • Voice matching from your real sent mail, not templates
  • Recipient-aware drafts that adapt to who you are emailing
  • Prompt Lab for version-controlling and A/B testing your persona prompt
  • BYOK support: bring your own API key for Claude, OpenAI, Grok, Mistral, and more
  • Works in Gmail and Outlook on the web, plus a standalone browser widget
  • Training data export and full data portability

Who uses it

Professionals who send high volumes of relationship-critical email: lawyers, financial advisors, recruiters, account executives, founders, and anyone who wants their inbox handled without sounding like a chatbot wrote it.

Pricing

Free tier includes 10 drafts per week with no credit card required. Paid plans start at $12/month and include unlimited drafts, custom persona prompts, and auto-draft.

Sideline

$ Details
-
Platforms
-
Release Date
-

ForthWrite

$ Details
freemium $12.0 / Monthly (Standard plan)
Platforms
Web
Release Date
2026 June
Startup details
Country
United States
State
California
City
San Diego
Founder(s)
Curtis Boortz
Employees
1 - 9

Sideline features and specs

  • Cost-Effective
    Sideline offers a secondary phone number for a fraction of the cost of a second traditional phone line, making it an economical choice for small businesses and freelancers.
  • Flexibility
    Allows you to have a separate business line on your personal smartphone, helping to keep work and personal calls distinct without needing another device.
  • Carrier Integration
    Calls are made using your carrier's network, which can provide better call quality and reliability compared to VoIP services.
  • Features
    Offers valuable features like auto-reply, voicemail, number porting, and team number sharing, which enhance its functionality for business use.
  • User-Friendly Interface
    The app has an intuitive and easy-to-use interface, making it accessible even for users who aren't tech-savvy.

Possible disadvantages of Sideline

  • Carrier Dependency
    Relies on your primary carrier's network, which may be a limitation if you have poor reception in your area or if you're on a constricted mobile data plan.
  • Limited Advanced Features
    Does not offer as many advanced features as some VoIP-based services, like call recording or extensive analytics.
  • Subscription Cost
    While more cost-effective than a full second line, it is still a monthly subscription cost, which can add up over time.
  • International Limitations
    Primarily geared towards U.S. and Canada use, which may limit its effectiveness for international business needs.
  • SMS and MMS Limitations
    Some users have reported issues with sending and receiving SMS and MMS, particularly with media files.

ForthWrite features and specs

  • Voice Matching
    Learns from your real sent mail, not templates
  • Auto-draft replies
    Replies waiting in Gmail before you open your inbox
  • Batch-drafting
    Draft replies for your entire inbox with one click
  • Works in browser
    Gmail, Outlook, and web browsers
  • BYOK support
    Claude, OpenAI, Grok, Mistral, and more
  • Prompt Lab
    Version control and A/B test your persona prompt
  • Free tier
    10 drafts per week, no credit card required

Analysis of Sideline

Overall verdict

  • Sideline is generally considered a good option for those needing a separate line for business or personal purposes. It offers robust features, but users should ensure it fits their specific needs and budget before committing.

Why this product is good

  • Sideline is a communication app designed to provide a second phone number for personal or business use. It brings convenience by allowing users to manage calls and texts separately from their primary number, offers features like voicemail, auto-reply, custom caller ID, and team numbers for business collaboration.

Recommended for

  • Small business owners who need a professional phone line.
  • Freelancers managing multiple clients.
  • Individuals seeking privacy by separating personal and work communications.
  • Teams looking for a solution to share a single contact number.

Analysis of ForthWrite

Overall verdict

  • I don't have verified information about a product called ForthWrite (forthwrite.ai). I cannot confirm its features, quality, or reputation, so I'm unable to provide an accurate assessment of whether it's good.

Why this product is good

  • No reliable data available on this specific product in my knowledge base
  • This may be a newer product, a niche tool, or possibly a fictional/hypothetical name
  • Providing details without verified information could result in inaccurate or fabricated claims

Recommended for

  • Unable to determine without verified product information
  • Consider checking the official website, user reviews on platforms like G2 or Trustpilot, and independent tech review sites for accurate details

Sideline videos

Sideline App Review for iPhone and Android 2020

More videos:

  • Review - Get A Second Number With Sideline Phone App!
  • Review - Get Second Phone Number on iPhone with the Sideline App

ForthWrite videos

No ForthWrite videos yet. You could help us improve this page by suggesting one.

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Category Popularity

0-100% (relative to Sideline and ForthWrite)
Communication
100 100%
0% 0
Email
0 0%
100% 100
VoIP
100 100%
0% 0
Email Productivity
0 0%
100% 100

Questions & Answers

As answered by people managing Sideline and ForthWrite.

Which are the primary technologies used for building your product?

ForthWrite's answer:

Next.js, React, Supabase, Anthropic Claude, OpenAI, Stripe, Vercel, Chrome Extensions API

What makes your product unique?

ForthWrite's answer:

ForthWrite learns your writing style from your actual sent mail, not a generic prompt. Every draft sounds like you wrote it because it was trained on how you actually write. It also auto-drafts replies before you open your inbox, so your email is partially handled before your day starts.

Why should a person choose your product over its competitors?

ForthWrite's answer:

Most AI email tools give you a blank box and a "write for me" button. ForthWrite builds a voice profile from your sent history and gets more accurate with every draft you edit or send. Unlike ChatGPT or Gemini, it works natively inside Gmail and Outlook with no copy-paste. Unlike Lavender, it writes the draft, not just scores it.

How would you describe the primary audience of your product?

ForthWrite's answer:

Professionals who send high volumes of relationship-critical email and cannot afford to sound generic: lawyers, financial advisors, recruiters, account executives, consultants, and founders managing their own inbox.

What's the story behind your product?

ForthWrite's answer:

Built out of frustration with AI writing tools that produce text that sounds nothing like the person sending it, and as a way to handle large amounts of daily email. The core insight was that your sent mail is the best training data you already have, and no tool was using it.

User comments

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Reviews

These are some of the external sources and on-site user reviews we've used to compare Sideline and ForthWrite

Sideline Reviews

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ForthWrite Reviews

  1. curtisboortz
    ยท Founder at ForthWrite ยท
    I built ForthWrite to fix generic AI email, and I still use it every day

    I built ForthWrite because I kept sending emails that sounded like they came from the same generic AI as everyone else. After launching it, I still use it for my own inbox every day, which is about the most honest endorsement I can give.

    The Chrome extension lives inside Gmail and Outlook on the web. Open a thread, hit Alt+Shift+D, and a draft comes back in your voice, not a template. The free tier is real: 10 drafts per week, no API key, no credit card. Voice matching is included on free, because that is the point.

    What keeps it useful compared to Gemini or a chat tab: it learns from what you actually send. Every edit you make before hitting send becomes a signal. Over time the drafts drift closer to how you really write, and the dashboard shows the improvement curve so you can see it happening.

    The web compose surface lets you draft from forthwrite.ai without installing anything, useful for people who want to try before committing to the extension.

    Standard adds recipient-aware and intent-aware drafting plus AI coaching. Pro adds auto-draft (replies waiting when you open Gmail), batch replies, and Prompt Lab for version-controlling your prompts. Teams adds a shared persona and seat-level analytics.

    ForthWrite is not for everyone. If you just need quick replies and tone does not matter, Gemini is free and already in your inbox. ForthWrite is for people where tone does matter: client communication, relationship-driven threads, external correspondence where sounding off costs something real.

    Disclosure: I am the founder and use it daily. Happy to answer questions in the comments.

    ๐Ÿ Competitors: Jace.ai, Fyxer, Mailmeteor
    ๐Ÿ‘ Pros:    Drafts land inside gmail and outlook; no copy-pasting from a chat window|Voice matching is on the free tier, not paywalled behind paid plans|No api key, no credit card to start; free tier runs on a server-side proxy|Learns from every edit you make before sending; drafts improve over time|Full keyboard flow: alt+shift+d to draft in any thread, no mouse required|Byok on paid plans, 9 providers supported, keys encrypted at rest|Web compose at forthwrite.ai works without installing the extension at all
    ๐Ÿ‘Ž Cons:    10 free drafts/week is enough to evaluate, not enough for a heavy inbox|Auto-draft, batch replies, and prompt lab all require the pro tier|Early-stage product; fewer third-party integrations than mature inbox tools|No mobile app: the extension and add-in are desktop-only (chrome on web, or the outlook desktop add-in)

What are some alternatives?

When comparing Sideline and ForthWrite, you can also consider the following products

Google Voice - Google Voice gives you one number for all your phones, voicemail organized in an email format, free...

ReclaimAI - Helps users prioritize their work and personal calendars

RingCentral - RingCentral is the leading provider of cloud-based communications and collaboration solutions for small business and enterprise companies

Superhuman - Superhuman is an email management tool.

ChucK - A strongly-timed music programming language

Shortwave - Email smarter & faster with a reinvented experience for your Gmail