What's the best solution for communicating with ~10 people on a group project?

Not email... Slack is the obvious choice, but looking for something messaging related that's more temporary. Coordinating with a group of 10-15 people for a couple of weeks.
Niv DrorWriter/Social Editor @ProductHunt · Asked
11
Asana

The task management tool, completely redesigned

BPlan4Uwww.bplan4u.co.uk · Written
This is a great "to-do" list that can be shared with everyone. you can @ people in your tasks or add them as a follower too. You have your own list and others can create their own (so you don't see everything in one hit, only tasks assigned to you). You can also create groups you can all share to :)
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