MBF

MBF (Marines Best Friend) is a source port created by Lee Killough after he left the Boom team. It is regarded by some as Boom's successor.

MBF adds several features:

• Friendly monsters, including single-player helper dogs
• Bugfixes, such as a fix for the blockmap limit (MBF includes an internal blockmap builder)
• A "beta" mode, in which MBF emulates the behaviour of Beta versions of Doom. This includes the BFG 2704, the version of the BFG 9000 included in the Beta.

MBF was originally licensed under the non-free Doom Source License, but Killough has since relicensed his work under the GNU GPL.