A few days ago Apple released its top 10 list of iPhone apps for 2010 and only one freemium app was listed as top grossing, Zombie Farm. Zombie Farm combines all the fun of Farmville with zombies (!), allowing you to plant either crops or corpses (seriously). You can then use the zombies you&'ve planted to attack your neighbors or pirates or aliens (no, I am not making this up).

Apparently this is a winning combination, as the game hit 7.3 million downloads in November, up from 6 million in October and growing about 25% a month. Currently it boasts about 2 million monthly active users, a number which has been doubling every couple of months since the app&'s launch this February. Users have spent 2.76 billion minutes playing the game, which have resulted in 61.5 million Zombie Farm invasions. And despite complaints about the most recent updates&' slowness in the iTunes reviews, the developers are obviously doing something right.

To the tune of millions of dollars. Playforge developer Vince McDonnell and his wife were in danger of a4s‚ losing their house when he built the app, and now not so much. While McDonnell will not reveal how much total revenue the app has made thus far (people pay for in-game currency like $0.99 brains and tombstones) in comparison, Doodle Jump, the 10 app on the top grossing list sold about 3 million units in five months at $0.99 each which would project to about ($) 7 million sold for the year.a4s‚ Zombie Farm was at number 6 on the list, which means McDonnell has made at least a few million thus far.

You can download the app here.