My certificate authority uses X-CA. This is a brilliant piece of software, very worth while if you looking for some "CA" software. Its very very flexible and complete, the only other thing i've seen that has come close in terms of features has been the Netscape iPlanet CA software (part of the j2ee and web server software they used to ship). But X-CA is capable of doing things i've never seen in alot of CA's before, and well worth a look.

Sadly the owner of the code seems to have decided it was "time to move on" which is a shame, but its probably going to be good enough for some time to come

My CA (original) is here
My New CA (2009) is here
My New CA's CRL is here