If you don't want to compile your own tcpcrypt, you can use the Mac OS X GUI wrapper, which includes the binary and is available at http://tcpcrypt.org/download.php.
Tcpcrypt does not depend on non-standard libs on Mac OS X, so just run:
cd tcpcrypt/user
./configure
make
Optional: running make install will install libtcpcrypt and tcpcrypt
headers, for building apps that use tcpcrypt's session ID.
The launch script (in tcpcrypt/user) starts tcpcryptd and sets up your firewall to send port 80 and 7777 packets through tcpcrypt:
./launch_tcpcryptd.sh
With tcpcryptd running, open http://tcpcrypt.org/test.php to try it out.
See the included README.markdown file for more ways to try out tcpcrypt and
for troubleshooting help.
See INSTALL-FreeBSD for firewall setup instructions. (FreeBSD and Mac OS X use
the same firewall, ipfw.)