Colobot - don’t think it was “shareware” but it absolutely came as a demo on ceebot.com (still hosted there today I believe). Literally THE game that got me into computer programming and whatnot.

Otherwise for actual shareware, I loved Jazz Jackrabbit 2, Crazy Gravity and some game unfortunately titled “Worm” (snake clone) with MIDI and sound effects still stuck in my head to this day

I really wanted to play a couple shareware games called Jetpack Joyride, and Hot Chix n Gear Stix as a kid, but neither of them would play on my Windows XP netbook as they had a hard check for if you were on either Windows 95 or 98, even with compatibility mode.