DIFF utility works for 2 files. How to compare more than 2 files at a time?

Displaying 10 files side-by-side and highlighting differences can be easily done with Diffuse. Simply specify all files on the command line like this:

diffuse 1.txt 2.txt 3.txt 4.txt 5.txt 6.txt 7.txt 8.txt 9.txt 10.txt

Vim can already do this:

vim -d file1 file2 file3

But you're normally limited to 4 files. You can change that by modifying a single line in Vim's source, however. The constant DB_COUNT defines the maximum number of diffed files, and it's defined towards the top of diff.c in versions 6.x and earlier, or about two thirds of the way down structs.h in versions 7.0 and up.