Haven't used any of these, but this is what a quick Google turns up: http://sdelements.github.io/lets-chat/ http://sdelements.github.io/lets-chat/ https://roc

Haven't used any of these, but this is what a quick Google turns up: http://sdelements.github.io/lets-chat/ http://sdelements.github.io/lets-chat/ https://rocket.chat/ https://rocket.chat/ https://mattermost.com/ https://mattermost.com/ https://zulipchat.com/ https://zulipchat.com/