The very popular Skype VoIP service has provided a Linux client for some years now, but it's not nearly as full-featured as its Windows counterpart, and right now it's a binary-only application. However, things may be partially changing at this company that's in the process of being spun off from eBay. There's a new blog post on Skype.com entitled Skype open source
. It's officially confirmed that "an open source version of [the] Linux client [is] being developed." This open-source client is part of some larger offering that supposedly will be coming down the pipe at Skype. These efforts will also help them get Skype adopted within Linux distributions and seeing Skype on other new platforms.
Before you get too excited though, it's very likely that the Skype protocol will remain proprietary but just the client above that will be open-source under an unknown license. We're waiting on more news from Skype as this may turn out to be quite interesting.