BG Render for a limited time is offered at an introductory price of $4.99 for the basic version and $19.99 for the pro version. These prices are set to go up in a couple of months to $9.99 for the basic version and $29.99 for the pro version which is still a great price for such a valued tool. Also be sure to check the AEscripts site for upgrade information.
BG Renderer is a script that allows you to render your Render Queue items in the background while you can continue working in After Effects. It runs as a dockable panel that is saved as part of your workspace.