Wirize - Payment checkout for freelancers

botwick - Build your own SMS-based text bot

Google Payment API - Enable an easy-to-use checkout experience for customers

Abot for Slack - Trusted by over 1000 Slack teams ✅. Abot is a simple and highly configurable app for anonymous feedback messages and more. If you want to create a poll on Slack or use it as an anonymous suggestion box you just need to type a simple command.

Pay Me Or Else! - How to avoid and deal with clients who don’t pay (ebook)

Estherbot - Transform your resume into a bot.