Non-Linux FOSS: Tales of Maj'Eyal
I love gaming, but I have two main problems with being a gamer. First, I'm terrible at video games. Really. Second, I don't have the time to invest in order to increase my skills. So for me, a game that is easy to get started with while also providing an extensive gaming experience is key. It's also fairly rare. All the great games tend to have a horribly steep learning curve, and all the simple games seem to involve crushing candy. Thankfully, there are a few games like Tales of Maj'Eyal that are complex but with a really easy learning curve.
Tales of Maj'Eyal (ToME) is a top-down tactical RPG that feels a bit like Dragon Warrior from the original Nintendo. Yes, making that comparison dates me, but that age of gaming holds a special place for me, because it was the only time in history that I wasn't a terrible gamer! ToME has adventures, quests and an extensive game that honestly will take me years to explore fully. But that's okay, because from the first monster I battled, it was fun. Plus, while the gameplay reminds me of those Nintendo games of old, the graphics are detailed and impressive. And I'm not normally fond of video game soundtracks, but ToME has an incredible batch of music that sets a perfect mood. I'd try to embed a link to the audio here, but since it's open source and available for just about every platform, just go download it and give it a try.