Based on our record, Followup.cc seems to be more popular. It has been mentiond 1 time since March 2021. We are tracking product recommendations and mentions on various public social media platforms and blogs. They can help you identify which product is more popular and what people think of it.
I'll update this if I find more. For now, this seems to be a partial solution. It's a Gmail add on (except I don't use Gmail) that adds reminders. The options when setting reminders include cancelling it if someone replies, and to remind everyone in the thread. If you combine those two, it seems like — if you use Gmail's web client and have $23/month you're dying to get rid of — a decent way to add the feature. Source: over 1 year ago
FollowUpThen - The simplest way to schedule an email reminder
Future Me - Send an email to your future self
Gmelius - Gmelius is the first collaboration platform designed for G Suite and your company's daily tools.
Dabble Me - Your own private place to write. A journal/diary to help you remember what's happened in your life.
Right Inbox - Schedule Emails in Gmail To Be Sent Later
Letter to my future self - Letter to my future self is a prominent email scheduling service that gives you the opportunity to create a letter with goals and thoughts for your future self and schedule a date for sending it.