Keychat is just one of many options for NIP-07 signing. Alby, nos2x, and a couple others are out there, as well. NIP-07 is the most universally adopted signing standard for all Nostr web apps. If you are building a PWA, then order of priority would probably be NIP-07, then NIP-46, and finally NIP-55 since it is Android specific.

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That order of priority changes drastically if you are building a native Android app, though. Then you'd better have NIP-55 working out the gate or go home. Add NIP-46 when you can get around to it, and no need to bother with NIP-07 since the app isn't operating in a browser.