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
2
Glip

Real-Time Team Productivity

John WangDirector, Platform Products, RingCentral · Edited
Like Slack for chat but well suited for group projects with integrated tasks, calendars, etc. Free with great UX.
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