The full original, in fullscreen

What it is: the complete first game, not a cut demo
Included: nights 1-5, the sixth night, and the custom night with AI sliders
Controls: mouse - cameras, two doors, two hall lights
Screen: fullscreen button under the frame
Cost: free, no download

Play the full original version of FNAF (Five Nights at Freddy's) online, in fullscreen. Nothing is cut and nothing is locked - this is the whole thing, from the first phone call to the custom night.

What "full version" means here

All five nights, in order, with the phone calls intact
Night 6, which unlocks once night 5 is done
The custom night, where you set each animatronic's AI from 0 to 20
The death minigames and the ending screens
4/20 mode - everyone at maximum, the challenge the community built its reputation on

Most browser versions of the first game stop after night 5 or drop the extras. This one does not. If you want the same game with the full write-up, character list and survival tips, that is the FNAF 1 page, and the sequel that removes the doors entirely is FNAF 2.