I am developing a p2p application using Flex based on RTMFP (ciruss server).
One of the peer will run on Linux and other Peer in windows.
Will all the version of Linux support Flex development.
it sounds like you're asking two different questions.
Flex builds your application into a .swf. your application runs in Flash Player, so it will run on any platform with Flash Player.
Flash Builder, the graphical IDE for creating Flex applications, appears to be available for Mac and Windows. that means you can use Flash Builder on a Mac or Windows to build an application that will then run on any platform with Flash Player.
the no-cost open source Flex SDK, with which you can build Flex applications, appears to be available for Mac, Windows, and several versions of Linux.