We are currently using trac and have become dependent on one of its features. Within the source browser, you can press View Changes and see all the diffs between 2 revisions. And we love being able to download a zip file that contains all the files modified, in their directory structure.
Is there another open-source application that can do that?
It's very easy to get the same result using just commandline svn. You could write a script that will get those values for you if your new trac-replacement won't have that feature. Here's the demo script in bash:
#!/bin/bash
// replace 100 and 120 with revision numbers
svn diff -r 100:120 "svn://path.to.your.svn.repo" > svn.rev.diff
gzip svn.rev.diff
This will give you a nice gzipped diff file (svn.rev.diff.gz) between two revisions. Of course you could add some params to it instead of hardcoding the numbers but that's just to show how this can be done.