[nuclearnerd]

Basecamp is great, and free for educators as mentioned. They recently added an instant messaging system called pings ( to better compete with Slack) and we use it all the time for private conversations.

The one thing I've found is that there are so many features, you need to implement a bit of team policy to keep it useful. Most importantly, conversations should be kept in their own message board threads, and people should be careful to make sure only the right people are on the notification list. Since all replies are "reply all", information can be quickly buried in "me too" or other unrelated posts if you're not careful.