How Many "Duke Nukem"games Are There And Where Can I Find Them?

There are a number of games in the Duke Nukem Series. Which are Duke Nukem, Duke Nukem II, Duke Nukem 3D, Duke Nukem Forever etc. If you are interested in knowing more about the series and downloading them, you can log on to the official website of 3D realms. The link is:
www.3drealms.com