If you're desperate for a discord-like experience (because lets face it, irc and mailing lists arent very flashy anymore!) you can try:

• rocket chat - General purpose chat platform, very similar discord
• mattermost - developer-centric platform, similar to slack
• Matrix - open protocol, has a bunch of desktop clients

~~Yes you wont have voice/vodeo chat for these but IMO that's rarely useful anyway. And if you DO need it then you can use stuff like teamspeak or zoom***~~

~~***yes i know the issues with these options but for devs you dont really ever need to use meetings for very long and sometimes using a shitty free service with all you need is better than self hosting your own. Maybe Nextcloud talk can work?~~

Some good arguments made for FOSS voice/meeting apps, and why VC and meetings are more important to the FOSS workflow than I thought :)