Clay is the typed, revision-controlled filesystem vane (kernel module) and also contains Urbit's build system (formerly a separate vane called Ford before it was merged into Clay). Clay's revision control system is similar to Git.
Clay contains a number of desks, which can be thought of as separate repos or branches, and contain the source code for your apps. The
%base desk contains the Arvo kernel and vanes including Clay itself, as well as the standard libraries.
Clay is located at
/base/sys/vane/clay.hoon within Arvo.