Linux/Unix in general, mid 1996, MkLinux part time on my Mac. I soon picked up a SPARC ELC (running Solaris) for $50 plus another $50 for the seller to put a fresh OS install on it, then a Pentium Pro HP server new but cheap when the Pentium 2 ones came out (1997). So GCC for PowerPC and x86 from that time. And emacs, which I first used at work on Sun in 1006 I think. And obviously GNU make was in the mix there.
I was already familiar with Unix-style tools from BSD on a Zilog Z8000 at university in 1984 and then Apple MPW (Macintosh Programmer's Workshop) from late 1986.
Obviously I've used various IDEs along the way (Think Pascal, Zortech/Symantec C++, CodeWarrior, Visual Studio on NT 3.51 and 4, VSCode, Eclipse, XCode)
But it's a huge thing to be able to use familiar tools with familiar features on everything from a $3 Milk-V Duo (1 GHz 64 bit RISC-V, 64 MB RAM ... much bigger and faster than my early SPARC and x86 Linux machines) up to servers worth tens of thousands of dollars, not to mention both local and remote (e.g. AWS) machines.
I'd much rather be told "add X to CFLAGS and Y to LDFLAGS" than have to hunt through nested dialog boxes to manually find the right checkbox to select. Not only to set up the same configuration as someone else (or a web site etc) but also to compare setups. With option strings you KNOW there isn't some obscure checkbox in a buried dialog that you forgot or never found. Thank goodness IDEs these days at least store that stuff in XML or JSON or something, which can be stored / transmitted / put in source control / hand edited even if it's nearly unreadable.