Competition Winner picker - is there something to download to pick the winner?

[Overseasmom100]

My friend is running a Facebook Competition where people have to comment. She wants to pick a winner fairly - Is there something she can use online that selects the winner?

I think if you google rafflecopter there is one and it might lead you to other ones

Assign each entry a number starting at 1 upwards, then do a number generator to pick one out of the numbers assigned?