Yes, but some have taken games from other sites and said they were thiers.
That's because those games were theirs. If you want a game on this site that isn't already here, talk to one of the staff members about it, like Carlie. Then she can talk to Dan and he might be able to get a hold of the games creators to see if the would like to publish the game here.
If it is your own game, click submit at the top and fill everything out, then click submit. Any questions other than that can be found in the FAQ.
Also, many threads have been made like this. It is best to do a little research and get an answer over creating a thread that has already been created.
