I was playing Avernum 4, and the vanhatti refered to his peoples mages as "Shapers". looking back through the game relationships, is it possible that the shapers from geneforge found refugee far underground and ascended into the vanhatti of the Avernum Saga? Considering that the ability to shape one selves was an ability held by the Shapers (albeit, outlawed), this is completely feasible. This could be the Aver-Forge link some were looking for.
-edit: Conversation: "I am what you would call a.. a politician. I am not a Shaper. a wizard, i mean."
also, would anyone care to discuss the fact that there are down right Gazers in Avernum? and not just some variety of monster like the drakes, these Gazers (and some eye-beast) act exactly like the ones from geneforge, are resistant and spew the same things, control minds of others, etc. These frighteningly intelligent, and seemingly immortal creatures could of easily lived throughout the ages.
Also, they use a stick that nullifies the shades so that they don't attack the person wearing it. this is discribed almost identically to the "control rods" used in geneforge 1, and by the mad mystery shaper character in geneforge 4 (or 5, i forget)
Most evidence points to the fact that Geneforge is a prequel is Avernum.