I saw it recommended here. I've been using it for a couple of weeks and am happy with it. I use it on an Android phone. Here's the web site: http://downdogapp.com/. Source: over 2 years ago

Yoga really has been a big help for me. Not a cure all but a great first step. There are endless you tubers you could watch (just find someone you vibe with) but my favorite way is downdogapp.com. You can use it on your phone or laptop and it is very customizable. I have the paid version but if I remember right the free version was excellent. But really there are endless free places to find beginner yoga. I... Source: almost 3 years ago

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