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While a majority of web games from 1998-2009 were made with the Adobe Flash IDE, the SWF format has since become open and a variety of frameworks and tools have emerged (many of them free) to facilitate game development! If you're interested in any of these platforms, here is a place to sample games made with each one.

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  flixel A collection of games made with the flixel framework!
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  FlashPunk Featured games made with the FlashPunk library!
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  Stencyl Featured games made with Stencyl.
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  The Games Factory 2 Featured games made with The Games Factory 2.
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  Construct 2 Featured HTML5 games made with Construct 2.