Plenty. Most famous one would be Nextcloud. I'm running that for years, and am very satisfied with it. Coming with "core functionality" like file storage, calendar and contacts, it has addons (called "Nextcloud Apps" for quite a lot of use cases – including your todo list (Tasks), a password manager (Passwords, Passman), and many more.
If your are looking for open source games. I think you should definitely checkout the Python Games repository.
This below repository has a good collection.
Although it is not Open Source since it has Apache License.