The Linux Kernel is propably the best working example for open source.

Personally I had the most exciting experiences with open source games, like Super Tux Cart, OpenTTD, 0 A.D.
Once I watched a streamer playing OpenRCT2, but the Twitch integration server, which allows to have the names of the people in chat appear in the game, was offline. Because the game is open source, I was able to have a look at the API, write my own server in a couple of hours and share it. Was a really funny stream then!

Wine is a great project, too. I really like the idea that people cooperate with each other to bypass commercial limitations and on this way be able to play their favourite games on a free operating system.