If I don't want to put my private keys into more than one product but also want to use mobile clients, what are my options? Is there yet an (open source of course) Android app I can use that would sign and decrypt for me regardless where the other client needs it? I know there's a nip for that but I never got around trying anything out, so I end up posting on Twitter as I can't post on Nostr while on my phone only.

#askNostr 

 I don't understand, why don't you want to input your nsec into more than one app? 

 Every app can leak it to hackers or outright steal it at will. I'd pretty much not want to have to rotate my key, especially as that's not yet a thing in nostr. So for now, only the nos2x browser extension knows my keys. 

 Yes I know what you mean but my opinion is that it is more important to use nostr and risk your key than to use twitter instead. It will come. 

 There is https://github.com/greenart7c3/Amber which is supported by Amethyst and there is also https://play.google.com/store/apps/details?id=com.nostr.universe which may host multiple progressive web apps.