Ruby packaging tool that compiles Ruby and your source code into a single binary, with a virtual file system inside and a patched Ruby that transparently requires files from it. Produces one executable (~30MB) with no need for a host Ruby or gem install. Original author stopped maintaining it around 2021; community forks exist, including one announced on Reddit that embeds Ruby 3.1.3. Cannot cross-compile — binaries must be built per OS/arch (Mac for Mac, Linux for Linux), and because not everything is statically linked, binaries may not be portable across Linux distributions or older Ubuntu versions.