https://github.com/fosscord/fosscord
📬 Spacebar is a free open source selfhostable discord compatible communication platform - GitHub - spacebarchat/spacebarchat: 📬 Spacebar is a free open source selfhostable discord compatible commun...
looks like an interesting project
Why not just contribute to Matrix, which is already well established and tries to 'discordify' their ecosystem, too?
In my view, what this ultimately is is a free Discord client. The server is there because I assume the developer liked Discord's API and wanted to be able to self host a server using it, but I imagine the majority of users will be interested in using this client with discord.com.
Keep in mind that "don't use proprietary platform, switch to x/y/z" doesn't account for the unfortunate reality that people may have contacts on that platform and switching wholesale and cutting off contact with those people is an unreasonable tradeoff. While a completely free service would be ideal, using a free client with a non-free service is still an improvement.