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.
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.