Most people know that:
Asterisk is the world’s leading open source telephony engine and tool kit. Offering flexibility unheard of in the world of proprietary communications, Asterisk empowers developers and integrators to create advanced communication solutions...for free.
Asterisk is released as open source under the GNU General Public License (GPL), and it is available for download free of charge. Asterisk is the most popular open source software available, with the Asterisk Community being the top influencer in VoIP.
But actually installing it may still be daunting. Enter AsteriskNOW:
AsteriskNOW is a Software Appliance; a customized Linux distribution that includes Asterisk, the AsteriskGUI, and all other software needed for an Asterisk system. The world’s leading open source telephony engine and tool kit, Asterisk, can now be easily configured with a graphical interface. AsteriskNOW includes all the Linux components necessary to run, debug and build Asterisk, and only those components, so installation is easy. You no longer have to worry about kernel versions and package dependencies. Unlike other Linux distributions used to deploy Asterisk, no unnecessary components that might compromise security or performance are included.
With AsteriskNOW, there's, er, now no excuse for not giving it a go.