At my current work place, Skype and Lync (or Skype for Business) are what we used for team communication. It works great until we need to onboard/offboard people. I also need to set status to DO NOT DISTURB because I wanted to avoid the constant ding ding ding notification.

At a previous workplace, Skype and IRC are used (IRC are for mass communication, whereas Skype is more for personal-level communication).