What is a good OSX incremental backup software (not time machine) So I used to use CCC to clone my external drive to another external drive for a backup copy. 

What I realized is that I want incremental backup that is versioned. So I can go back to a copy that is on a specific date in the past. 

I don't want to use time machine for this because right now TM is already being used to backup my main drive to a time capsule. 

As far as I know, I can't setup TM to backup my main drive to time capsule while choosing to backup an external drive to another location. 

I guess I'm looking for 3rd party solution here?
Take a look at Crash Plan. It allows you to backup to a disk, machine on the network, or the cloud. It has options for how long to retain items and what to ignore.