Another TUI Discord client written in Go, called 6cord [1]
I'm using Ripcord [2] because it is written in Qt, cross-platform, and works for both Discord and Slack. It also has voice chat support. It is not FOSS though, not feature complete either, and against ToS of Discord and Slack.
What is it about Ripcord that violates Slack's ToS? AFAIK Slack are pretty accepting about custom clients, to the point where they even mention wee-slack [1] in their docs [2].