I've tried Slack, Ryver, Moxtra, RocketChat, and others, and this app is showing the most promise, mainly due to its ability to annotate images. I would however need three key features for it to be my top choice:
1/ Ability to edit a post after posting
2/ Ability to do ad-hoc group calls (audio-only is fine; audio+screen-sharing would be ideal)
3/ Google Drive integration
Also would love to always view a post's comments in threaded view, or flattened but with option to sort by most recent comments first (reverse chronological)
Bonus: Integrations with Gitlab, Jira, and the like