Jon Blow’s videos about the development of his new game are really interesting. To build the game he wants to build, he decided to create the language he wanted to use to build the game (kind of like Mozilla created the language they wanted to use to build a browser). Blow’s language Jai has not been released, but Jorge Rodriguez has created a primer for the language based on Blow’s videos:
Jai is a high-level programming language developed by Jonathan Blow, creator of indie games Braid and any-time-now-to-be-released The Witness. It is an imperative static/strongly typed C-style language, but with a variety of modern language that C lacks. Blow began work on Jai in late September 2014. It is still in development and as of yet is unavailable to the general public. Blow developed it with an eye towards video games, but in fact it’s a general purpose programming language that could be used for any task.