So what is Halo Custom Edition (HaloCE) you ask? Simply put, it is a new version of HaloPC that is free for all HaloPC owners. This unsupported version of HaloPC is a stand alone Gearbox Software release and is not supported by Microsoft.
So what is the purpose of HaloCE? HaloCE was created as a way for Gearbox to introduce a bunch of new features to HaloPC. The most important of which is the ability to play user created content. Along with HaloCE we will also be releasing a set of tools, tutorials and source art which we call the Halo Editing Kit (HEK). This is a powerful package which will allow users to create their own custom content for HaloCE.