DJGPP was foundational for me. It got me into C at an early age, as the second toolchain I spent much time with following Microsoft QuickBasic, and it was my gateway to eventually exploring Linux and Emacs.

I'm sure many others here have similar stories. It was especially valuable to have something like DJGPP back in the mid 90s, when many of us only had access to DOS PCs and compilers were expensive.