Click this link to enter the libemu homepage, download your copy, and enjoy the first open source shellcode detection engine using emulation.
It has been a lot of work, it took a lot of time and it is not complete yet, libemu based detection modules for honeytrap, nepenthes and snort are still todo.
In the meantime you can enjoy the great shellcode detection commandline utility sctest to detect and profile shellcodes in suspicious dumps and create graphs of it.