Turtl :
https://turtlapp.com/
There is a web app, an android/ios client...
It's open source :
https://github.com/turtl
If you want you're own server :
https://turtlapp.com/docs/server/
>Turtl lets you take notes, bookmark websites, and store documents for sensitive projects.
Why three main functions? IMHO I'd be way more interested if it just did one thing well.