(A little late, I know... but better late than never!)
I'm on the team responsible for the clc.stackoverflow.com domain/app.
Jason's answer is essentially correct. That domain is used for our in-house ad server, which currently serves these things:
Originally, those job ads were served by the Careers application. We decided in late 2013 to split the serving of those listings off into its own project with a dedicated team, so that we could do cool things like use Providence to show our users jobs that are better suited to their interests. We wanted to be able to explore and test different strategies without being tied to the development cycle of either the Core Q&A or Careers teams.
So, why the domain? Early on we went with a Futurama theme for the project (our team chat room is called Planet Express), and the name of the web application that lives at that domain is Calculon:
clc was chosen as the domain prefix simply because it's a 3-letter mnemonic for "Calculon". It doesn't actually stand for anything.
We're planning on putting some information up on the homepage explaining what the domain is used for and other informative things. We just haven't gotten to it yet.
Hope that clears some things up!