Virus

Infect, evolve, repeat: Virus.

Drag'n'drop your virus on red blood cells, but beware of white blood cells and antibiotics. After each level, you may enhance your virus (better reproduction, higher defense, and so on).

Doctor Who - Cyber Assault

An original Risk variant set in the Whoniverse: Doctor Who Cyber Assault.

You control the "Preachers" who fight to free the world from the Cybermen. On the world map you can move troops from one of your territories to another, attack a territory that's either free or controlled by the Cybermen (battles are fought using a rock-paper-scissor mechanic), or recruit new troops (one per territory, so the more land you've got, the more troops you'll gain).
If you win a battle against the Cybermen at one of their bases, the game changes to a shooter: you infiltrate the base to destroy the transmitter. This "mini-game" is probably the worst part of the game: it's really slow and not even that interesting. The main game is nice though - if you like Risk, that is.

Swords and Sandals

Manage a gladiator: Swords and Sandals.

It's a very simple roleplaying game. Combat is played in rounds. A lot of luck is involved. Still, it's fun now and again.
There's a sequal too.

Bunker

Defend your, well, bunker in: Bunker.

This point-and-click game takes some time to get any challenging.

Cosmic Crush

Think of this as flOw with more game attached: Cosmic Crush.

You control an asteroid/planet and try to absorb other asteroids smaller than you to get larger. If you hit something that's larger than you: Game Over. Once you reach a certain size you enter the next level.

Armadillo Knight

Keep rollin': Armadillo Knight.

Be a sword-wielding armadillo and fight trolls and stuff to save a bunch of bunnies...

Zombie Horde 3

Awful lot of fun: Zombie Horde 3.

You walk thru a city infested by zombies - and you get paid to kill them. With the money you earn you buy better weapons (or upgrades), ammo and armor. Some of the weapons are needed to advance the plot - for instance, pretty early in the game you need a shotgun to destroy a barricade.

While the graphics are somewhat minimalistic, the controls are great (mouse plus keyboard), and you're able to save your progress.