Server-side development

Server-side scripting
Node.js - JavaScript
Redtamarin - ActionScript 3

BaaS (Backend as a Service)
Parse
Amazon EC2

RTMFP Service
Cumulus - C++,Lua
ArcusNode - Node.js

Articles
FlashRealtime - tomkrcha - Flash P2P
Peer-assisted networking using RTMFP groups in Flash Player 10.1
The Node Beginner Book

Sources
NetGrouper
AS3MUL