Looks like a good project, I may give it a try on Windows.
On Linux, I use weechat to connect to a local bitlbee for Discord and Hangouts. When I was using Slack I used wee-slack [0] with success, but it looks like bitlbee has a plugin for Slack, too [1]. This lacks a few of the features of Ripcord (e.g. voip, graphical emoji, emoji completion), but it works.