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
Download blabber.im from the Google Play Store or F-Droid
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
Windows: unofficial alpha Windows builds (Does not currently check for updates, Keep up to date with the RSS feed)
And done! Make sure to check the lock icon at the bottom-right is set to OMEMO to keep your messages encrypted.