Personally:

Nextcloud (file backup and so much more, I use it to backup files from my computer. Might explore some of the other features soon)

Immich (image backup, I use it to back up photos from my camera + phone)

Radicale (CalDAV + CardDAV for calendar and contacts sync)

Forgejo (GitHub alternative, and the backend of Codeberg! I use this as a local backup to my git repos in addition with cloud backup with Codeberg. They work nice together, when you set two remotes per git repo)

Vikunja (to-do list syncing, don’t use this anymore as I mostly use Joplin for this now)

Joplin (Markdown editor, supports cloud sync with nextcloud, I use this for both notes and to-dos!)

I used to run ConvertX (to convert any file type, whether it’s document, image, video, etc. Think a self-hosted CloudConvert), but I somehow messed up the user permissions and couldn’t log in (100% user error on my part), so I didn’t bother.