If I understand correctly the project, which I didn’t knew, I think the main difference with obtainium is that this one is portable and work on multiple platforms, not only Android. Linux, Windows and MacOS are listed.

Otherwise there is also litube. It’s not the same concept and thus less privacy friendly but it might be useful too. This is a webview customized for YouTube with an ad blocker, player to play in background and many other functionalities.

Personally, I found Kavita and Grimmory far too complex for my use and also very resources hungry. At the end CWA is just perfect for me. Still have to configure my kobo e-reader to use it directly and this will for sure be a game changer from my current solution which consist in converting epub to kepub with kepubify and then put it on a local webserver that I open through kobo web browser.

Update: Kobo sync configured and it’s just awesome, just adding book to a shelf and sync the reader as usual and hop, everything downloads and progress updated in cwa.

If it has to be water resistant, why using chalk instead of paint? Real question, not trying to make fun.