SourceGear offers their 3-way Diff/Merge tool for free. DiffMerge is an application to visually compare and merge files for Windows, Mac OS X and Unix.
Product Features (from their Website):
- Diff. Graphically shows the changes between two files. Includes intra-line highlighting and full support for editing.
- Merge. Graphically shows the changes between 3 files. Allows automatic merging (when safe to do so) and full control over editing the resulting file.
- Folder Diff. Performs a side-by-side comparison of 2 folders, showing which files are only present in one file or the other, as well as file pairs which are identical or different.
- Configurable. Rulesets and options provide for customized appearance and behavior.
- International. Compatible with 42 different character encodings.
- FREE. Full featured. Not a demo!