Holga 120N is the most simple and basic model in Holga 120 series. It doesn't have a flash but it has a hot shoe, so you can use any electronic external flash on it.
The Holga 120PC 3D stereo camera is a lensless camera that allows you to take pinhole shots using 120 film. Double pinholes capture 2 images simultaneously giving you a pinhole image in 3D.
The principle of pinhole cameras is to let light pass through a very small hole which hits the film directly causing exposure without passing through any lens.
Holga 120CFN is similar to Holga 120FN, but it has some interesting features. It has 4 different colour filters in front of the flash, red, blue, yellow and original (no colour/white).
Holga 120GCFN is similar to Holga 120CFN, but has the additional feature of a glass lens. This can provide sharper image quality when compared with plastic lens.