Marco Polo Video Walkie Talkie is an up-and-coming free video chat option from Joya Communications. You can chat as much as you want, OR as little as you want: the app provides the ability to stop and resume conversations when appropriate, and if one participant is busy, they can simply send video replies to each other and chat when it's convenient.

Add in some other features, like Instagram-style filters, and Marco Polo Video Walkie Talkie is a cool all-rounder video chat app.