SIP Express Router (SER) is a very fast and flexible SIP (RFC3621) proxy server. Written entirely in C, SER can handle thousands calls per second even on low-budget hardware. A C Shell like scripting language provides full control over the server's behaviour. It's modular architecture allows only required functionality to be loaded. Currently the following modules are available: digest authentication, CPL scripts, instant messaging, MySQL support, a presence agent, radius authentication, record routing, an SMS Gateway, a jabber gateway, a transaction module, registrar and user location.