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
5
Facebook Messenger

Facebook's standalone Messenger for the web

Nick Abouzeid🕴6Social & Growth Intern @ProductHunt · Written
Easy to use, and the event feature works as an efficient way to remind people of when/where they should be at all times (if you go through the trouble of setting them up)!
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