Their free version of Labyrinth recently hit the number one spot in the App Store's most downloaded and has since settled at fifth place. Illusion Labs reveals that this level of popularity translates into approximately 80,000 downloads a day.
The company uses the free application as a 10-level demo version of their $5.99 full version [App Store]. The developers were also responsible for a popular free game called iPint which was commissioned by ad agency Beattie McGuiness Bungary for Carling beer. (The iPint application is currently unavailable in the U.S. App Store)