With this webapp, anyone can call you from a browser from anywhere in the world at no cost to them. The rates are really low for you, too, but you can also get credits (equivalent to one euro) and accumulate virtual money to use instead.
Dialzoo is a great alternative for making business or other phone calls without having to post your phone number on any public webpage or social network. Also, the good thing about this tool is that if you don't pick up, there's an online voicemail option available, completely free of charge.
The way Dialzoo works is very simple: just sign up with your email and link your phone number. Once you receive the verification email, you can share this link to use the service: firstname.lastname@example.org. The calls are of good quality and generally reliable.
The computer must have a microphone or be connected to one.