Glad you asked. We use Matrix/Element to chat with each other, a decentralized instant messaging protocol/platform. Think of it as a discord but fully encrypted and without shitty telemetry. Its encryption is based on the Olm and Megolm cryptographic ratchets. Now, if you've been on this website for a decent amount of time, you'll notice we previously aimed to use XMPP, but after some tinkering and thought, we concluded that it isn't a good platform to communicate with, since we couldn't use encryption in our chatroom due to the encryption working only if the said chatroom is private and with other parameters we couldn't use. Plus it was pretty complicated for newcomers since one would need to find its own XMPP host, and more. Come and join us!
I'd recommend you check this page. You can either use the web version or install the app on your dekstop, or even your phone (using either f-droid or playstore). You just have to create an account, and slap the link at the bottom of the page in your browser to join us!