Jellyfin: An unfederated alternative to Plex, with some pros and cons. Very lightweight, customizable with plugins. Decent iOS and tvOS client from the devs.
The Lounge - got like 7 people using it basically daily to chat
Lemmy, even though I'm the only one really actively using it.
E-Mail server, I don't get a whole lot of mail but it's a pretty important one!
Everything else tends to be a lot more idle, but I've also got NextCloud, an IRC server, soon a Matrix server, an internal VPN so all my devices can always talk to eachother no matter where they are.
I've considered Airsonic but I haven't found a good client that looks good and doesn't behave weirdly. I had one launch about 500 threads trying to transcode the same song which ate up my CPU time on my server resulting in a stern e-mailing from my host.
Plex, PiHole, Photoprism, Home Assistant, Syncthing in a hub and spoke config, Caddy for reverse proxy, custom containers for: yt-dlp, restic, and rsync.
There are multiple ways to evaluate usage. I’ll go with what I would guess is your desired measurement, things that I use intentionally (as opposed to things like dns, which just happen incidentally to other things or automation based things which are continuously running but not necessarily interacted with):
Mastodon
An app I’ve written to collect personal data
Jellyfin
Lemmy
Bitwarden (I pay to self-host as opposed to vaultwarden as the latter probably won’t have a security audit)
Using 'hours of use' as the metric, it would be Plex. The ones I use every day are Libreddit, TT-RSS, Huginn and Reddit-RSS - and my own journalling app and pocket clone.
Like most, Plex and the *arrs are the main ones, paired with overseerr
Others I use daily or frequently are:
Benotes for bookmarks and quickly saving links for later
Gotify so I have push notifications of anything that happens on the server
Koillection as an inventory of all my knitting and crochet digital patterns
Homepage this one is always a pinned tab on any browser and a shortcut on my phone, quick glance of my services with the widgets and just a click away from them.
Also hosting a minecraft instance with backups but so far no dashboard or anything
I don't see Docspell mentioned anywhere, but it's really cool document management system. Similar to Paperless, but with pretty easy way to extend functionality via addons if you need to add some extra automation when ingesting the documents.