yes it is. Rails, django, git, etc. were all developed to build something that makes money. 37Signals was building Basecamp when rails was created. Django was

yes it is. Rails, django, git, etc. were all developed to build something that makes money. 37Signals was building Basecamp when rails was created. Django was for news websites. Rails isn't why Basecamp makes money. It was just a useful thing that happened to come out of the development of Basecamp. Build your product. Charge for it. If you happen to build something cool while working on your product and it is NOT core to your business idea, give it away.