A strange answer, but I find a lot of fan games and game mods good examples of this. You've got an individual (or perhaps even an entire team) working for free

A strange answer, but I find a lot of fan games and game mods good examples of this. You've got an individual (or perhaps even an entire team) working for free on a project that could potentially be shut down at any time with no expectation of any compensation other than other people enjoying their work. For example, the SMW ROM hack Brutal Mario (whatever you may say about the level design quality) is an insane technical achievement. https://www.youtube.com/watch?v=INa41RSwiCc https://www.youtube.com/watch?v=INa41RSwiCc The fact some random Japanese guy no one knows the identity of spent 10 years turning a single game into a strange crossover title with hundreds of technical gimmicks based on other games (including some uses of mode 7, 3D, etc) is nuts. A team of 20 or more people working full shifts might have trouble replicating a lot of the stuff in this game. Or how about Project M? Before it was shut down, they basically turned Smash Bros Brawl into a clone of Melee with new mechanics, stages, characters, graphics and music, pretty much everything: https://www.youtube.com/watch?v=rcJHZCuaG84 https://www.youtube.com/watch?v=rcJHZCuaG84 Or heck, Mushroom Kingdom Fusion in general. It may be an extremely buggy, often poorly balanced game, but damn it's a crazy ambitious premise with a level of variety not seen in pretty much the entire industry outside of it. https://www.youtube.com/watch?v=rD7VWxHGU4o https://www.youtube.com/watch?v=rD7VWxHGU4o 300 levels, around 10 or 20 characters with their own play style and mechanics, about a hundred power ups, thousands of enemies and bosses, even more random gimmicks and level mechanics and a massive amount of graphic and music from everything you can think of. All by what? Less than 20 people in their spare time? Either way, the fact people can work on stuff like this purely in their free time and ending up dedicating years of their lives to a project that can be on par with a commercial one without any means of making money off of it... that's got to be pretty impressive. And I haven't even mentioned that guy whose spent so long on his mod that Duke Nukem Forever actually started and finished production while it was still in development. With said project still being ongoing and unlikely to finish within the next few decades.