Free VoIP, make and receive IP Telephony calls. ineen
has a laundry list of features which include voice, video, instant messaging, and most important - free. It is definitely a viable alternative to Skype and it has a nice interface. It is also available for Windows
and Mac OS X
. Try it out, its pretty nice!
For those interested in offering their own simliar product, ineen was built using Xten's eyeBeam SDK.