An interface between Haskell web frameworks and web servers.
A Haskell web application targets WAI and then can be deployed to any backend with a WAI adaptor. The premier WAI backend is the Warp web server.
WAI also adds modularity and code-sharing through middleware and WAI applications. Code can be written that works with any web framework targeting WAI.
http://www.yesodweb.com/book/web-application-interface [http://hackage.haskell.org/package/wai](Haddock Documentation)