MakeMMO

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On this website you can post MMO, the cost of the game is really cheap for such a thing because it is making unlimited items, you can create an economic game, there are many interesting systems, such as
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The plan - when the game is economical objects can be put to any player, and in that object will infuse eg coffee, etc..
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Courses - probably do not need to explain, they can add statistics (eg attack, defense, etc.).
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Missions - probably everyone also knows what's going on missions in which you have to do something to give a value for it.
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Jobs - work a few hours, receive money or other values.
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And much much more.