Is there a hidden or alternate ending for the game Limbo?

The only thing you get after the credits is an achievement.

And no, there is no hidden ending in Limbo. If you beat the game without dying once you'll get another secret egg (and is required to get 111% in the game, but there's no achievement for that), but otherwise there's no secret ending.

Actually there is a secret level. It can be accessed after collecting all 10 hidden eggs

{This is ONLY on the PS3/PC or later versions of the game. (I play it on iOS and PC and it does work for this-i am not sure if they added it to the original Xbox version, but you should be able to find out if the "door" is there or not (see below...) }

After you have all of the eggs, go to chapter 26, just before the arthropod (the mosquito-insect you snatch a ride on.) Go in the dark past the spot where you get the "Alone in the Dark" achievement. You will see a big metal door with a circle of 10 candles in front of it where each candle represents an egg. Once all are lit the door will open and you can enter the "secret" level.

https://steamcommunity.com/sharedfiles/filedetails/?id=113463434