They already have very experimental Linux support. You have to build whole app yourself though. I’d say that in month or two we’ll get a binary. You can track Linux porting progress in this issue

I believe they don’t store any credentials on the server. If you really don’t trust them you can also host your own instance. You can read more here

WefWef works great as a web app. Just open wefwef.app in your browser and click install in browser context menu.