FNAF: The series that just won't die
Given the fact that the series spawned merchandise, books, and even a movie (still being filmed). It probably never will.
I mean it also helps that people have made so many fan-games of it or used it's mechanics like:
One Night at Flumpty's (1 and 2)
Those nights at Rachel's
Five nights at Candy's (1,2, and soon 3)
The Joy Of Creation (Rebooted)
Five Nights in Anime (1 and 2)
Shift at Fazbear's Fright
Five Nights at the Krusty Krab
Five Nights at the Chum Bucket
Unreal shift at Freddy's
Five Nights at Sonic's
and that's still not all of them...