diff utils in Linux

I needed to diff directory structures in Linux to look for differences between source trees for an application. I used the diff util in Linux with some success, but decided to try some of the GUI tools available through the apt repos.

1. xxdiff - This one is probably the oldest gui util I tested, but it was the most capable for what I needed. It's an old xwindows app that requires two arguments when executing... something like this:
   xxdiff
   for basic use. From there, configuration is quite robust. It requires diff to be installed.
2. kdiff3 - This one has a steeper learning curve, but also includes the ability to merge differences. I didn't need most of this functionality.
3. synctree - I didn't explore this too deeply. It is a command line util for syncing directory trees... I got that from the name, too.