Look nice, good documentation, community support, seem like a lot of build-ins features, demo site is very responsive! The admin area use lot of iframe!
WebGUI is modular, powerful, secure, and user-friendly. Most users find themselves managing content within hours, and developers can easily plug-in functionality to maximize a site's potential.
Linux, Tru64, Solaris, AIX, etc.
Apache 2 with mod_perl