How many different satellite navigation systems are there?
As of 2007, the United States NAVSTAR Global Positioning System (GPS) is the only fully operational GNSS. The Russian GLONASS is a GNSS in the process of being restored to full operation. The European Union's Galileo positioning system is a GNSS in initial deployment phase, scheduled to be operational in 2013. China has indicated it may expand its regional Beidou navigation system into a global system. India's IRNSS, a regional system is intended to be completed and operational by 2012.
Source: Wikipedia entry for Global navigation satellite system
There's a couple more (France's DORIS, Japan's QZSS), too.