I have a MediaWiki instance on my laptop (I've found the features of all other wikis/mindmaps/knowledge databases decisively insufficient after having a taste of MW templates, Semantic MediaWiki and Scribunto).
Also some smaller things like pihole-standalone, Jellyfin and dictd.
Primarily as a personal knowledge database, but also management of what, how and when is to be done (not for reminders or external motivation; rather to form a mental picture and understand the priorities). In future, I'll also use it to track the state of various ongoing affairs as the need arises, and perhaps integrate local programs and APIs into the wiki pages (that's probably where I'd need to write custom MW extensions).