Today we had a discussion about generic swiss army knife tools:
- Apache and the mod_rewrite module. That is applying regular expressions to URL, Cookies, query elements, etc… It is effectively a router to be able to rewrite URLs, change destination of the requests based on URLs, change headers, etc…
- mailfromd for sendmail (or any other milter filter). This effectively allows you to do a lot of online checks in realtime to help you to fight against spam.
- OpenSer, now split into OpenSips and Kamailio. I see this the equivelent of the mod_rewrite module in the SIP world 
- Non opensource, but to the same level you can do also do protocol manipulation for LDAP with the LDAP Proxy from Sy
Sure that there are others, but these are really useful for the things that we do…
