OpenXES, the open source implementation of the XES event log standard, was originally distributed with source code in the tarball. Later versions, including 2.26, are class-only jarfiles.

The source is still available, but it’s not linked well on the site. You can find it at the Eindhoven repo at https://svn.win.tue.nl/repos/prom/OpenXES/trunk/, or through a richer UI showing some recent source control context.