Settled on Zulip to replace Jabber based system. Rocket.chat, matrix/riot, mattermost, Zulip, and likely others were tried. Zulip's 'topics' (think threads) w

Settled on Zulip to replace Jabber based system. Rocket.chat, matrix/riot, mattermost, Zulip, and likely others were tried. Zulip's 'topics' (think threads) was the feature that put them ahead of every other system. Free push notifications were a plus as well. If threading isn't important, check out Mattermost. If you're into federation, matrix is something to check out.