I'm looking for a TCP/IP stack that can be used without an OS. Our customer has an "aversion" to interrupts and doesn't want a real OS on a embedded board we're building. It's desirable to move as much of the functionality to FPGA as possible due to the fact we will be only using a 50 to 100 MHz Arm. And I'm pretty sure GPL licensed stuff won't be acceptable for this client. (Due to the legal quagmire associated with it. They expect to have full unrestricted rights to the software once it's complete.)
uIP (micro IP) and lwIP (lightweight IP) are both candidates worth consideration. According to the original developer of both stacks - Adam Dunkel - one of the primary differences between the two is: "lwIP is larger than uIP, but provides better throughput". Both stacks employ a modified BSD license and have been used in commercial products.