What are common diff tools?

Common diff tools used for comparing files and directories include:

diff: The standard command-line tool in Unix/Linux for comparing text files line by line.
```
diff file1.txt file2.txt
```
vimdiff: A visual diff tool that uses the Vim editor to show differences side by side.
```
vimdiff file1.txt file2.txt
```
meld: A graphical diff and merge tool that provides a user-friendly interface for comparing files and directories.
Beyond Compare: A powerful commercial tool that allows for detailed comparisons of files and folders, with support for merging changes.
KDiff3: A cross-platform tool that can compare and merge two or three files or directories.
P4Merge: A visual merge tool that helps in resolving conflicts and comparing files.
colordiff: A wrapper for diff that adds color to the output, making it easier to read.

These tools vary in functionality, from simple command-line utilities to advanced graphical applications, catering to different user preferences and needs.