Defender

Brief guide
Defender is a quite simple game in which you must buy, place, and upgrade people to stop monsters from reaching the portal at the end of the path. Monsters will always follow the path, and units can only be placed on the walls. However, some units shoot faster than others, and some monsters move faster than others. Once a unit has been placed, it can't be moved, although you can sell it for half the price you bought it for.
There are four different categories of units: Rangers, Psychics, Mages, and traps. There are four units of each type, but you will have to upgrade categories to unlock more units of that type. Click on a category at the bottom of your screen to upgrade it.
Traps work like other categories, except you place them on the path instead of the wall. They will damage enemies who walk over them (unless, of course, the enemy flies over them, for example birds and bats).
Once a unit has so many kills, it will show an upgrade symbol. This means it is ready to be upgraded to the next level- for a price, of course. Click on a unit with the upgrade symbol to level it up.
Even if this doesn't sound simple, don't worry. It's easy to get used to!
________________________________________
NEW (May 16th 2009):
Just a quick 10-minute update requested by my brother to make GMs more, uh... Obvious. No change in gameplay at all. Sorry for the disappointment. :)

NEW (April 10th 2009):
A minor but important update, as well as changing the colours of Defender's interface very slightly, I have been tracking down a very discreet loop in the code, which caused the game to begin to lag more and more immensely after about 20 minutes of playing. I don't know if it's been fixed; I'm going to have to do some online testing with other people first... So, let's get hosting, people!
Oh, yes, and there was a small glitch where the Void trap's price was shown to be 520g, but it actually cost 540g. It has now been set to 520g, and my apologies for not noticing this sooner!

NEW (March 7th 2009):
Well, when I heard about this "awards" thing yesterday, I just couldn't wait to take advantage of it in a cheesy way! So here it is:
-Awards for completing each difficulty of Defender. Temporary GM for anyone who can get all 5 medals - it's nearly impossible ;)
-I was working on this. But I might as well let it out so far. 5 new waves with a strange surprise at the end! (Yes, that makes it even harder to get the medals. Don't worry, though.)
-Now entering well-drawn territory!! Yes, after wave 30, the REAL drawings come in. And I've got waves up to 60 of this lined up, with huge thanks to Redmoon30! Some big shockers in line! Heheheh...