I didn't say Gosu was proprietary. They've taken this whole "open-source" catchphrase and made some CIO's, that generally don't know anything other than budgets and bodies, feel better.

It does, however, tie you completely to the Guidewire platform/products. A very smart move by the company. It will be decades before these slow-moving behemoths will rip out this language that was a blip on the radar. That doesn't mean it was needed or is as historically important as the devs seem to think.