This DHCP server (written in Python) was originally developed to diagnose a DHCP problem which turned out to be an incorrectly configured netmask, but has proven useful for other DHCP-related debugging as well, and to have a handy DHCP server which doesn't need any configuration.
A typical run looks like this:
./demodhcpd.py -i eth0 --my-ip 10.123.45.1 --ip-range 10.123.45.10-10.123.45.200
demodhcpd can simulate the behavior of different DHCP servers. Pass in -s isc to switch to simulating the behavior of the ISC DHCP server.
In contrast to other DHCP servers, demodhcpd does not meddle with your network configuration in any way.