DeltaChat, the email-based messenger
I'm pretty sure that most of the Gemini users would enjoy an email-based, encrypted and free messenger.
This already exists and it's called DeltaChat Messenger.
Here's the official website:
Why this project is great?
It's a great software because you can use your email account in a signal-like messenger app. You don't need to register or give your phone number to anyone. You just need an existing email address and you can chat with other users also if they don't use DeltaChat!
Take a look to the official website and give it a try. I'm sure you will like it. It's also e2e encrypted!