Super-K makes use of svn to share and manage code between multiple users. The source code for the SK libraries (as well as various other documents and file) all lives in an svn repository. The code can be "checked out" of the repository, and then compiled and run on various operating systems. Modified code can be checked back in for others to use. Subversion keeps track of different modifications from different users, and can merge them appropriately.
The Subversion website gives full information on how to use svn, but here a few useful commands:
svn co https://kmcvs.icrr.u-tokyo.ac.jp/svn/rep/skofl/trunk skofl
svn commit -m "Comment on what the change was" filename(Always, always give comments for your changes!)
svn diff -rHEAD filename