Content filtering app

[Michael Hipp]

Anyone know of a good Internet content filtering application to run on a 
Linux router?

I presume it would need to have access to some kind of subscription 
service to keep the rules and black/white lists up-to-date.

I'm aware of ClarkConnect and SmoothWall but I was looking for something 
  that is just an app rather than requiring me to use their whole 
package. (But if nothing else turns up that's a good 2nd choice.)

Thanks,
Michael