The very first UNIX version I ever worked with was Microsoft Xenix. This was followed by various UNIX versions from hardware suppliers such as HP, Nixdorff and ICL. The advent of the 386 so the emergence of SCO UNIX. The first Linux I installed was 0.95. At the time, a few floppies were a basis and everything had to be built up from source code. With today’s distributions, this is hardly necessary anymore. Outside of software, I have also used Linux for firewalls, mail servers, web servers and asterisk-pbx.
The first thing I developed for UNIX/Linux was a Videotext Terminal Emulator and the last RMC 2.0.