Here's a list of Non-Open Source web apps: https://www.neoito.com/blog/best-progressive-web-apps/
Here's a list of Open Source web apps: https://en.m.wikipedia.org/wiki/List_of_free_and_open-source_web_applications
The barrier of entry for these apps are just so low. You don't have to download anything for them to work and (for now) they're crossplatform.
If you haven't yet, you might want to try voyager on your lemmy instance: https://vger.app/
This is talking about the WiiU version.