1. Dropbox Paper for easy note-sharing. We've got a ton of docs we share, update, and constantly reference to
2. Appear.in - https://appear.in/ - probably the best team conference software we've used. We compared it to Slack, Skype, Hangouts (which is horrible), and a few others. Appear.in always won out, plus we can use it with contractors/clients without the need of an account. Works really well from the phone, too.
3. Org Mode - a recent addition, we've been using org mode to plan out dev sprints and story out features before putting them into PM software
4. Slack - self-explanatory