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

If you're looking for a good spin-off, mari0[0] is a really fantastic Super Mario Brothers-meets-Portal game. I just wish development had continued and provided more levels. [0] https://stabyourself.net/mari0/. - Source: Hacker News / 9 months ago

If you're cool with 8-bit Mario, there's a Mario fangame called mari0 that gives Mario a portal gun. Source: about 1 year ago

There's a Mario fangame called mari0 that gives Mario a portal gun and allows up to 4 player hotseat multiplayer. Source: about 1 year ago

Mari0, the Portal/Super Mario Bros crossover was made with Löve2D so yes, it definitely can as any other framework/engine. Source: over 1 year ago

Lol. But in seriousness finding time and motivation to play everything I've downloaded would be wonderful. Unfortunately time is limited. I still seek to preserve what I can. My favorite mario fan game has always been and always will be Mari0, a Mario + Portal crossover which has remained free to access for 10+ years at https://stabyourself.net/mari0/. It could be because of nostalgia though. Super Mario... Source: over 1 year ago