In no particular order, and not all are EU or FOSS But most are FOSS. I think only the first 6 are both EU and FOSS clients. I may not have marked all of the Self Hosted ones, but I think I did.
- https://www.mumble.info/
- https://movim.eu/
- https://twake-chat.com/
- https://sylkserver.com/
- https://fusion.privmx.com/en
- https://matrix.org/ecosystem/clients/matrix-commander/
- https://fluxer.app/ (self hosted)
- https://a.weird.one/
- https://zulip.com/
- https://sharkord.com/ (self hosted)
- https://spacebar.chat/
- https://element.io/en
- https://teamspeak.de/
- https://stoat.chat/ (self hosted)
- https://jami.net/
- https://www.rocket.chat/
- https://mattermost.com/
- https://xmpp.org/ - https://roguesecurity.dev/blog/xmpp
Nothing to do with illegal, you want your privacy kept intact and your data to be your own. Data can be used in millions of ways to manipulate you, cheat you out of your hard earned cash and affect you psychologically. Don't forget, many VPN's are owned by the same companies that own the review sites and are about as trustworthy as an Israeli ceasefire.
https://www.cnet.com/tech/services-and-software/3-companies-control-many-big-name-vpns-what-you-need-to-know/
https://cyberinsider.com/vpn-review-websites-owned-by-vpns/
https://cyberinsider.com/kape-technologies-owns-expressvpn-cyberghost-pia-zenmate-vpn-review-sites/