According to some comments they're connected with VoipBuster but they have different FREE countries you can call with their Application. The idea is like Skype where you have your buddies you double click on to talk, but you can dial any number for free just like with VoipBuster.

According to a lot of sources, VoipBuster and NetAppel are owned by the same swiss company. NetAppel.fr adds the following countries for you to call free; Belgium, France and Switzerland. Canada, Italy, Netherlands, Portugal and UK have been removed recently.

I have not been able to setup IAX or SIP to use them although a ping responds to sip.netappel.fr and iax.netappel.fr.