Good free games you play for a long time?

[zort]

I recently started a list much like this in my notes file ^^ (I've trimmed it down a lot for this post)

• Tremulous (online FPS)
  
• Space Station 13 (online roleplaying (not RPG, roleplaying (think mafia)))
  
• Stranded 2 ("survival" (the quotation marks mean it's easy))
  
• Dwarf Fortress (low-level (i.e. detail-oriented) city building)
  
• Soldat (online 2D shooter)
  
• N (platform)
  
• Mu-cade (push the other snakes off the block before they push you off)
  
• Antigravittaatori (flying saucer (controls like a helicopter in thin atmosphere) racing)