Macromates deciding to open source it and make it available to the community for free under a GPL3 License. Macromates hopes to spark interest in free projects as well as in commercial ones with the possibility of a upcoming commercial useable license.
"I am also a pragmatist and realize that parts of the TextMate code base is useful for other (non-free) applications, so I may later move to a less restrictive license, as is currently the case with the bundles. For now, please get in touch with us if there are subsets of the code base you wish to use for non-free software, and we might be able to work something out." (Source)
It is available on GitHub and you can download and compile it yourself. The toolchain required is quite extensive and if you run into the error:
bin/gen_build:391:in `dynamic_lib': undefined method `' for nil:NilClass (NoMethodError)
You need to clone the git repository instead of just downloading the source, i have no idea why this is happening.