On the page it says it'll probably be $4.99. So it is open source, but it may not be free.
For the uninitiated (as myself): "“Free software” does not mean “noncommercial.” A free program must be available for commercial use, commercial development, and commercial distribution. Commercial development of free software is no longer unusual; such free commercial software is very important. You may have paid money to get copies of free software, or you may have obtained copies at no charge. But regardless of how you got your copies, you always have the freedom to copy and change the software, even to sell copies. "
Perhaps I also need to be initiated to comprehend this...
And in response to the last line of the README, it loads and builds absolutely fine in Xcode 3.
No. All free software is open source, but not all open source software is free software. The conditions for calling software "open source" are weaker than those for "free software".