I don;t think fortnight is open source, but it's been a while since I ran it - and I wonder if parts of it are using open source models and such.
I commented on the parent comment because I read it as sarcasm / inferring that a free game without free at is not free - and that something like that could never be modern or successful.. so I was trying to offer a counter point to consider which is similar - although certainly not exact apples to apples.
No sarcasm. I really mean what I wrote. The reason: this would open up a new market and encourage studios to develop open source games. Also, I really do not oppose proprietary art. Not even Stallman is against it[0].
We've had a bit of it a some years ago when some indie devs sold through "humble indie bundle" pay-what-you-want and made the code available if they money passed a threshold amount.