vidma is a utility for manipulating virtual disk images. It can show basic information about the image or resize it. Resizing is done by in-place modification of a file holding the image or by creating modified copy of such file. The only currently supported format is VDI (Virtual Disk Image), mostly used by VirtualBox.
phpVirtualBox is an AJAX implementation of the VirtualBox user interface written in PHP. As a modern Web interface, it allows you to access and control remote VirtualBox instances. Much of its verbage and some of its code is based on the (inactive) vboxweb project. It was created for people who prefer not to have to log in to their headless VirtualBox host to administer their virtual machines.
The virtualbox-COM Ruby gem is a library that provides a low level Ruby binding to the VirtualBox API, allowing anyone to control VirtualBox from Ruby code. It can create, destroy, start, stop, suspend, and resume virtual machines, and also list virtual machines, list hard drives, network devices, etc.