0compile creates a binary from source code, either for your own use or ready for publishing on the web through Zero Install. It can use Zero Install to download any build dependencies (compilers, header files, build tools, etc).
This is useful if there is no binary for your platform, or if you wish to modify the program in some way.
If plash is installed, it is used to sandbox the build so that it can't accidentally modifiy any files outside of the build directory.
For a full tutorial, see 0compile's homepage.