There's no bots I'm really missing hard right now, but it's worth recalling that bots are such a popular approach on Reddit specifically because the community has no way to improve reddit directly. If you want to add a feature to reddit, the ONLY way you can do it is to try to parse the text in a post/comment and the have the bot post it's own output as a comment or whatever.

With Lemmy, the code is open source and you can improve it directly. So before writing a bot to hammer the apis of an instance reading every post/comment made to a community, it's worth asking oneself if Lemmy could be improved to natively do the thing without needing a bot. Like for remind-me, what if Lemmy had a native remind-me button that direct-messaged you with a link to a post after some configurable delay. Easier to use, more efficient, no bot needed.

Now, this might be more work than writing a bot. And a bot can be a useful way to prototype some feature. It also means learning rust and JavaScript rather than python, and it means cooperating with Lemmy devs who might have concerns about performance at-scale, maintainability, or user-experience. These concerns will likely make the result better though. It's fine to do stuff via bots, but consider the possibility that directly contributing to improve Lemmy would be a better result that isn't possible in the Reddit ecosystem.