The article lists some of the tools that have been used to create MySQL. This is an important list which has helped mould what MySQl is today.
They helped provide an excellent compiler (gcc), an excellent debugger (gdb) and the libc library (from which strto.c has been borrowed to get some code working in Linux).
They have helped provide a really great editor/environment.
They are the author of valgrind, an excellent memory checker tool that helps find a lot of otherwise hard to find bugs in MySQL.
They have helped with the DDD (The Data Display Debugger) which is an excellent graphical front end to gdb).