Urban Terror
free fps, online multiplayer, a bit like counter strike but with more advanced movement (you can slide across the floor or climb etc)

zero-K
free rts, online multiplayer, a bit like total annihilation or surpreme commander but more fast paced
needs a "real" 3d graphic card though: if your laptop only has some integrated intel thing there might be problems.

soldat
2d jump-and-shot game, online multiplayer
(costs money to register but fully basically playable even without)

Across and elastomania.

<3. Shame Elastomania changed the art style, because I preferred the original.

Evochron Mercenary

starwraith.com

All movement follows Newtonian Physics. Full economic system in each quadrant. Fully customizable ships. Multiplayer. Best space shooter I've ever played.

Quote from Hyperactive :

Across and elastomania.

Yes! Elastomania!

Limbo
Crazy Machines 2
Legend of Grimrock (I guess should work fine on older machines)
VVVVVV

Arcanum. Basically the old fallout (1&2) type of game set in fantasy environment where you can play as mage, brute or technical character.

Pong
Tetris
Tic Tac Toe
Minesweeper
etc.

here's a small list of what runs on my ASUS T91MT (with an Atom Single core), other than LFS.

Grand Prix II (or any DOS games for that matter, and I got my g25 to work with it, thanks to DOSBox)
Bananoid (another DOS game)
Re-Volt
Half-Life
Half-Life: Blue Shift
Half-Life: Opposing Force
Midtown Madness 1 and 2.

Anything that is emulated that runs on a modern smartphone should run on a netbook.

Quote from Forbin :

http://information2share.files ... -worthwhile-dos-games.jpg

Quote from -NightFly- :

list of worthwhile dos games

You must be a redditor.

Elastomania is a hit! Remember playing it at the school hehe.
And btw, the moongame thing made me laugh, "derpderpderpderpderp" lol

Plants vs. Zombies