I went looking for this particular compressor, and discovered that 7-zip isn't in the tree, nor could I find it in a cvs attic, nor in the ports@ archives. It has a makefile.openbsd, so at some point, some porting work had been performed.
It compiles cleanly, and is LGPL licensed, except for the unRar plugin, which is freeware. Does anyone know why this isn't already in the ports? I thought I would work up a port for this, and submit it for review unless there is some reason why a 7zip port would not be accepted.