This is what I found online
- vboxautostart-service: manage some autostart options like configuration file, deny access to users, ...
- vboxdrv: the only one needed if you want to run virtualbox in the traditional way!
- vboxweb-service: needed if you want to use phpVirtualBox to access your VB machine from a remote terminal
- vboxballoonctrl-service:
Starting with VirtualBox 4.0.8 a new host executable called VBoxBalloonCtrl is available to automatically take care of a VM's
configured memory balloon (see Section 4.8.1, “Memory ballooning” for
an introduction to memory ballooning). This is especially useful for
server environments where VMs may dynamically require more or less
memory during runtime.
VBoxBalloonCtrl periodically checks a VM's current memory balloon and
its free guest RAM and automatically adjusts the current memory
balloon by inflating or deflating it accordingly. This handling only
applies to running VMs having recent Guest Additions installed.