ais523 is a European mathematician and esoteric language creator. His most famous creation is Underload, but he has a lot of other interesting languages listed on his userpage User:ais523. He also maintains a modern Intercal interpreter.
ais523 also takes part in some software projects that aren't deliberately esoteric.
- He is a developer of the Nethack game since about 2015 and its fork Nethack4 and acehack since about 2012. These are a challenge because the organization of the source code originates from the 1980s before modern coding practices.
- aimake, a build tool for C programs that scans the linker symbols of object files to figure out what dependencies to link with each main executable. He used this to untangle nethack, in which some of the C source files are generated dynamically by auxiliary programs built by nethack, and the source codes overlap so much that small changes can easily cause circular dependencies.
- ayacc (darcs repository at http://nethack4.org/projects/ayacc ) is a new implementation of the traditional yacc parser generator.