3rd party software

Databases

SQL

RADIUS (AAA) servers

RADIUS

Telephony Softswitches

• Asterisk

• OpenSER OpenSER is now Kamilio and OpenSIPS. wtf

• FreeSwitch looks really promising

Control Panels

• DTC/GPLHost looks nice

also

• GNUPanel
• OpenPanel
• ispCP Omega
• RavenCore

Virtualization

• OpenVZ
• Linux-Vserver
• Xen
• KVM...