If you prefer something offline and where the data is on your own computer I made EasyOrg [0]. It saves everything in text files in org-mode format. It's mainly for personal use. There is no support for collaboration. Syncing can be done to your other computers as you like, for example Syncthing, Dropbox, pCloud, git, NAS or whatever. Backup is also easy as it's the same as you hopefully already have today.

[0] https://easyorgmode.com