Oracle har just released VirtualBox version 4.3.22. This is a maintenance release with primarily bug fixes.
As you might know, Oracle has a number of pre-built virtual box images available for download, among them:
One thing that's missing from the official list is a normal database without CDB and PDB. However, the old 11g database image has not been removed yet - there just isn't a link to it anymore. But you can still get to it by following this procedure:
You can't just click the download link, because it goes straight to the image and you get an error that you haven't accepted the license.
Another option, you can download the Oracle 12c database image and then simply use dbca to create a non-cdb database (presumably there is enough space and memory in the image to do so).