Video conferencing
In the area of video conferencing or Teleconferencing, there are some big names like Webex or Citrix's "GoToMeeting" (wp:GoToMeeting) that garner most of the market share. However, newer technology has pushed the envelop of what's possible, as well as pushing down costs to make video conferencing more ubiquitous. Enter the free software video conferencing systems. Right price, fuller technology support and more features than proprietary systems. The truly "free software" video conferencing market is a relatively unheard of category, but raising eyebrows for venture capitalists and telecommuters alike.
While pure wp:VoIP systems like Asterisk handle telephone requirements, other software comes into play to deliver the whole enchilada of video meetings. One such company was DimDim, but they got swallowed up by Salesforce back in 2011. What makes these new applications compelling is that they not only allow voice communication, but they also do video and allow desktop or application sharing between groups (not just a two-party phone call). The age of telecommuting is here.
Some in the "no cost" category can be pretty good choices if you accept their limitations. Skype is in this category. They were acquired by Microsoft, and are largely regarded as a listening device for the NSA. So, if you don't care who is listening in on your calls, then Skype could be right for you. Google Hangouts could be good for you if you don't ever need more than 10 people in a call.
For enterprise use, GNU Gatekeeper is GPL licensed server software that compares to proprietary offerings like Zoom or BlueJeans
