Flowdock

Flowdock is well suited for small teams and to environments that doesn't need too much reliability. I think it has some management problems that can make your life difficult if you have to manage a big amount of users. If you want just a tool communication with basic features (without using any integration or robust features) it can be suitable for you. You should try Flowdock using its free version for a small team and compare with others similar products. Flowdock delivers team chat and collaboration features, but is not necessarily the best product. Maybe some usability problems that disturb me won't be so relevant to you.

The fact is, Slack is in place to be better product. They're the big dog in town and are moving toward a public offering. I think CA Flowdock has a nice mobile experience and generally works the way it's supposed to but major competitors like Slack are pushing the envelope on API integrations and bot builds that automate a lot of great features. I think Flowdock approaches things from a more corporate stand point while Slack is casting their net toward smaller companies looking for cool features.