MFGG (Mario Fan Gaming Galaxy) is a non-official Mario-devoted fangaming site. The site contains fangames by its various members, and it also gives out tutorials on how to make them. Most of the games in MFGG are made using Clickteam's 'The Games Factory', which is free to try but not to buy.
Also, a side-program is Game Maker, but very few use it. There are also the Message Boards, currently serving around 1100 members.
'Mario Soccer' by Kitsune Yamato (Fangames section)