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
GetStream.io - APIs for the development of scalable newsfeeds and chat applications.
FollowUpThen - The simplest way to schedule an email reminder
BeHuman.Online - A more friendly and intuitive approach to virtual events. BeHuman.Online offers personalized virtual lounges and custom branding for an authentic event experience.
Gmelius - Gmelius is the first collaboration platform designed for G Suite and your company's daily tools.
Bevy - Scalable global events community around your brand
Boomerang for Gmail - Boomerang for Gmail is a Firefox / Chrome plugin that lets you take control of when you send and receive email messages.