worphco, if you can find any free (or even paid) product that has at least 50% of VoipNow functionality, just name it.
3cx - A Windows PBX, tageted to corporate users.
trixbox, elastix - Asterisk GUIs.
VoipNow is not an Asterisk GUI, it's business solution. It uses Asterisk with its own applications to implement telephony functions. I could say much more, but I do not want to self advertise.
When you make a comparision, compare apples with apples, or at least compare cars in the same class.