In June of last year Phoronix delivered the news that
the Skype protocol was reverse-engineered and that there was already a working open-source code example for interfacing with Skype to send messages. While it seemed promising at first for potentially resulting in an open-source Skype client, the
Microsoft-owned Skype vowed to take action. In the end they
did go after the open-source / reverse-engineering work and now it looks like the project is dead, or at least terminally dormant.
Following the June announcement by the researcher that reverse-engineered an older version of the Skype protocol, various bits of technical details and code examples were published. Skype went after this work with DMCA take-down notices. When Skype informed me that they were going after those responsible for the work, it was described as "unauthorized use of our application for malicious activities" and "infringes on Skype's intellectual property."
The
skype-open-source blog is now dormant. The last status update was in early October, with the only posts since then being unrelated (a Christmas tree photo and a post regarding the end of democracy in Russia). The open-source Skype code is
housed on GitHub and there hasn't been any activity there in eight months. The Git repository itself is also empty.
While not as good as a proper open-source client, at least Skype for Linux has
SkypeKit with
a set of exposed APIs for external applications.