One is a combination circuit breaker and GFCI which is installed in the service panel instead of a regular circuit breaker. This type usually has a small test button on it, and it protects that entire circuit. This is good in some cases, but is a nuisance in the case of older buildings. Another type of GFCI is the receptacle type, which is installed instead of a conventional receptacle outlet. Another type of GFCI is the portable type which merely plugs into an existing three-prong grounded outlet and converts that receptacle to a ground fault protected receptacle.
Some models even come with extension cords for use around the outlet or in damp locations.