Free OCSP server for testing purposes?
The best free OCSP server is in the OpenCA package. Here is an example of creating a custom OCSP message. If you like java then you should use EJBCA.
I think windows has an OCSP server in the windows 2008 enterprise edition. I know it has other parts of the PKI. This isn't free.
Windows Server 2008 and 2008 R2 Enterprise Editions both have OCSP as an option when you install the AD Cert Services. You can use both for testing purposes for 180-days. Download available from Microsoft.