This time we talk about Red5, an open-source Flash Streaming server. If you are going to study and develop Flex application, you probably want to develop some kind of cool client-server application with audio-video streaming support.
The Macromedia's Streaming Server is (very very) expensive. Red5 is free, multi-platform (it's written in java) and almost compatible with the latest version of Flex.

I started working with Flex + Red5 about two weeks ago. The whole framework is a bit complex because it's a mix of  XML+Flash Action Script+Java Servelts. If you don't like javadoc documentation as much as me, good documentation lacks (or sucks, if you prefer), especially about Red5's internal architecture.

If i have time, i'll post few tutorials about how Red5, Flex Builder & Co. on a GNU/Debian Stable system.
Stay tuned!