VirtualBox and open source
Before version 4.0, there were two editions of VirtualBox: a full binary containing all features and an "Open Source Edition" (OSE) with source code. With version 4.0, there is only one version any more, which is open source, and the closed-source components have been moved to a separate extension pack.
See the Downloads page for details.
As of version 4.0 we also no longer require third-party builds of VirtualBox to be distributed under the name of VirtualBox OSE. However we do still kindly request that they be clearly marked as third-party builds in some way, and that the version string (the "VBOX_VERSION_STRING" build variable), which appears at the top of the log file, be changed to reflect this. One way of doing this is by setting VBOX_VERSION_STRING on the build command line, which might look as follows:
$ kmk VBOX_VERSION_STRING='$(VBOX_VERSION_MAJOR).$(VBOX_VERSION_MINOR).\ $(VBOX_VERSION_BUILD)'_my_distribution_name