A universal root. You mount it, and it's mostly Go source with the exception of 5 binaries.
And that's the interesting part. This set of utilities is all Go, and mostly source.
The /bin should be mounted in a tmpfs. The directory with the source should be in your path. The bin in ram comes in your path before the directory with the source code.
When you run a command that is not built, you fall through to the command that does a 'go build' of the command, and then execs the command once it is built. From that point on, when you run the command, you get the one in tmpfs. This is fast.