Lode Runner is one of the first computer games I ever played on my Apple ][e. I recently discovered that a developer of a "modern" version released in 1995 is giving it away for free. I'm on level 55 or so. So fun, especially unlocking the original levels. What a flashback! 1987 here I come!
Freeciv is a free open source clone of Sid Meier's Civilization series. Start with two settlers and an explorer and try to develop your civilization. Research mathematics or recycling to give your nation the technological edge. Fight off your enemies and conquer the globe, or strike peace treaties and win the space race. I have wasted too many hours playing this game. My best friend randomly mailed me Civ III several months ago, but I still prefer Freeciv.
The Battle for Wesnoth is another free open source game. This one is more of a fantasy epic where you lead your armies against the enemy to save the world. Or whatever the campaign designer has in mind. It's a pretty addictive game, although I haven't become especially skilled at it yet.
What's that you say? Studying for an actuarial exam? The present value of an annuity-due? The yield rate of a callable bond? One more level of Lode Runner and I'll get right on it!
—Jack