XMPP lets you chat with others in a secure and future-proof way that allows you to chat with people on other servers, like E-Mail. Much more detailed information is available at my messaging page

Messaging page

Download blabber.im from the Google Play Store or F-Droid

Google Play Store

F-Droid

Tap "create new account"

Enter a Username

Choose server from the dropdown menu, make sure the server is it is high up on the compliance list

Complience list

And done! Make sure to check the lock icon up the top of your chats is set to OMEMO to keep your messages encrypted.

Enable link previews in top right menu > Settings > Securitiy and data protection > Show previews of web links in chat

GNU/Linux: Dino

https://dino.im/

Windows: unofficial alpha Windows builds (Does not currently check for updates, Keep up to date with the RSS feed)

Unofficial alpha Windows builds

RSS feed

Click create account

Choose a high up server from the left side of this list(1) and type the server into Dino (you don't need to type the https:// part). Might not work with some servers, either choose another one or make an account on their website and sign in with yourusername@yourserver.com

(1)

And done! Make sure to check the lock icon at the bottom-right is set to OMEMO to keep your messages encrypted.

Dino Screenshot

Webpage version