in a limited government the government is limited by law
in a unlimited government the law sets no limits on the actions of a government
tyranny can result in an abuse of power such as the abuse military power against its citizens.
When there is a normal democratic limited government the government can not use force like police or military against protesters or other sorts of opposition. In an unlimited government or a tyranny the government can enforce its will on its citizens and almost nothing can stop it except an uprising or something similar.
One of the founders of Foursquare is Dennis Crowley. The other is Naveen Selvadurai. I know you didn't ask for both but I wanted to give them to you just in case. I hope this helps! (:
