Goblin paints your github calender green. It modifies your repository's date environmental variable to make commits in the past.
Goblin's main purpose was to help me learn the basics of running external commands (mostly git) in Go, so it requires Go compiler to function.
Make sure you clone the repo using ssh and configure github with your public rsa key (details here). In case you've cloned the repo using https, this might be useful.
For running the script, place goblin.go inside the repo and use:
go run goblin.go days
This will take a while.
This has been tested on Ubuntu 14.04 (trusty).