Oracle VM VirtualBox 4.2 offers some new features that narrow the gap between this open source software and VMware's...
Workstation for server and desktop virtualization administrators.
The market share for hosted virtualization is divided between the commercially offered VMware Workstation (or Player) and the open source VirtualBox. The latter has been my product of choice for desktop virtualization and testing, not just because it's free, but because it has enough of VMware's for-pay features to be a useful substitute.
Plus, each revision of Oracle VM VirtualBox has tapered the gap between the two programs. Version 4.2 is another major step in that direction. To make my case, here's a rundown of the new VirtualBox features, many of which either replicate existing VMware features or expand on them.
Automatic VM start on host boot
Many non-desktop virtualization environments support the ability to automatically start certain virtual machines (VMs) when the guest OS boots and the virtualization software starts. This VirtualBox feature is useful if you know you're always going to be running a certain VM with VirtualBox. You can arrange to have it auto-start with the program. It's doubly useful if you're running a VM in headless mode, where it's being used as a server or something similar.
Up to 36 network cards per VM
Earlier versions of VirtualBox were limited to eight network cards per VM -- the first four configured through the graphical user interface (GUI), and the other four configured via the command line. Oracle VM VirtualBox 4.2 ups the limit to a whopping 36, which makes it possible to run VMs that serve as, for instance, simulated network switches. Note that the GUI in VirtualBox 4.2 still only supports editing the first four.
Network bandwidth resource controls
Another useful network feature in 4.2 is the ability to limit bandwidth utilization by a given VM, so it doesn't saturate your network. There is currently no GUI for this option; it has to be done through the command line interface via the bandwidthctl command. The user creates a named rule, then sets a bandwidth limit (how many megabytes per second) for that rule. Different adapters can be assigned different rules, and multiple adapters can be pooled under a single rule so that the total bandwidth allotted to that rule is shared between them.
The bandwidthctl feature also lets you limit bandwidth use on a per-machine basis for disk bandwidth. This is a handy way to keep VMs from flooding your host's disk controller, although if it's not properly tuned it can cause VMs to perform poorly.
Another network improvement is that network cards in VirtualBox 4.2 now support virtual LAN (VLAN) tagging. This makes it easier for VM traffic to be segmented and routed, and VirtualBox VMs can now be placed into VLAN environments.
Note that for proper support of this VirtualBox feature, you'll need to also enable VLAN tagging in the network adapter within the guest. Sometimes this involves installing a manufacturer-specific version of a network adapter driver rather than the default Microsoft version. In my own use, my host's Intel 82579V adapter, which I bridged to the guest via an emulated Intel PRO/1000 MT Desktop adapter, worked with VLAN tagging as long as I also set VLAN support in the guest's network card driver settings. (It was actually enabled by default.)
Improved Windows 8 guest support
It shouldn't come as a surprise to anyone that one of the biggest uses for VirtualBox these days is trying out Windows 8. I started doing so with the first public test releases, and VirtualBox's handling of Windows 8 was balky enough that I eventually just dragged out a notebook I wasn't using and installed it on that instead.
But now, Windows 8 has gone gold, and VirtualBox's support for the OS has been polished quite a bit. One of the biggest improvements is graphics support, because Windows 8 draws a lot more on graphics hardware effects for many of its basic functions (for example, the new Start menu).
This is a small addition, but it's a handy one. Previous versions used to display all your VMs in a single list, without much organization. Oracle VM VirtualBox 4.2 allows you to group VMs and even nest groups for further subclassification. Groups can be collapsed or expanded, or zoomed in on.
Altering settings during runtime
Oracle VM VirtualBox 4.2 adds, however provisionally, the ability to change a VM's settings while it's running. You can't change processor or memory settings, but the network settings can be changed to some degree (presumably by simulating a disconnect of the hardware).
Added disk image support
VirtualBox has long been useful for reading multiple types of virtual disk images, and VMware doesn't support nearly as many third-party disk images as Oracle's product does. VirtualBox 4.2 adds support for a few new formats: VHDX, the Hyper-V disk format (albeit in read-only mode for now); QCOW (used with KVM; full support for version 1 and read-only support for version 2); and QED images (used with QEMU). This support makes Oracle VM VirtualBox 4.2 all the more valuable for connecting to and recovering data from dysfunctional VMs -- no matter what the platform.
I recently ran VMware Workstation and VirtualBox head-to-head on the same hardware for the sake of a little research. There's little question that, if you have the budget for it, VMware is still the market leader, if only because it's so widely used and broadly supported. But for those without the budget or with relatively modest demands, VirtualBox remains a strong contender, and version 4.2 makes it even stronger.