Matrix (Riot is the app you would install) is federated, free software, isn't tied to your phone number, and has optional OTR-like encryption (it's based on Signal's encryption but has much more solid group chat encryption). Also messages don't go through a single server (only the home-servers that are involved in the communication), so the OTR-defeating problem that Signal has (that you can defeat the repudiation of the crypto by watching the server logs) is not nearly as much of an issue. It also has VOIP and video calls, that are also encrypted.