FR released the source code for their tools in 2012, some of the concepts are described in the repo, e.g.: https://github.com/farbrausch/fr_public/blob/master/werkkzeu...

A couple of additional links from my bookmarks:

- The EXE packer : https://www.farbrausch.de/~fg/kkrunchy/

- Some tech details in "The Farbrausch Way to make Demos" slides : https://llg.cubic.org/docs/farbrauschDemos/

- Various related videos (search for ryg/chaos/fiver2): https://files.scene.org/browse/resources/seminars/code/

- Overview of their tools + misc links: https://adrianboeing.blogspot.com/2012/04/farbraush-demo-too...

- Some .kkrieger details: https://fgiesen.wordpress.com/2012/04/08/metaprogramming-for...

I loved .kkrieger. The best first person shooter 96kb ever produced! :) [1]

[1]: https://en.wikipedia.org/wiki/.kkrieger

.werkkzeug1 was also my first though while scrolling through the article