Your AppKettle still works. The app that came with it doesn't.
iFavine shut down and took the AppKettle service with it, which left a lot of perfectly good Wi-Fi kettles unable to talk to anything. Kettle Remote replaces that app. It speaks to the kettle directly over your home Wi-Fi.
There is nothing to sign up for. The app talks to the kettle on your own network and nowhere else: no servers, no analytics, no tracking, and no data collected about you at all. If your internet goes down, your kettle still works.
Several phones in one house can use it. The kettle only accepts one connection at a time, so the app lets go when you're not using it and tells you politely when someone else has it.
Coming to the App Store and Google Play. This page will link to both when they're live.
The kettle's protocol was never documented. It was worked out by unpacking the original Android app and reading what it sent, then rebuilt from scratch. Read how that went, if you like that sort of thing.