eul.im is a closed-source commercial lightweight chat client launched 6 months ago; the author spent a few months advertising on related discussions until snagging a bit of critical feedback. https://hn.algolia.com/?query=eul.im&sort=byDate&type=commen... https://news.ycombinator.com/item?id=15597468 (apparently it still downloads a 180MB embedded browser https://github.com/eul-im/eul/issues/60)

There is also https://github.com/bkanber/Slackadaisical (no development since initial October appearance) CLI and:

https://news.ycombinator.com/item?id=15597508 >nikisweeting: https://github.com/saenzramiro/rambox [...] https://github.com/meetfranz/franz [...] share one Electron instance for all your chat services