Recs.
Updated
Open Source differencing and merging tool for Windows. WinMerge can compare both folders and files, presenting differences in a visual text format that is easy to understand and handle.
SpecsUpdate
Pros
Cons
Con Development is spotty
The latest version (2.16.0) was released in November 2018. Before that the last official release was made in 2013. The 2.16.0 is actually one of the two forks (Winmerge-v2-jp) that were kept maintained throughout the years, it just got named as the official release.
The other fork, WinMerge2011 is still being actively developed too. It's on par with the historical version, and has additional features such as showing only differences and a 64-bit version.
An 'official' list of forks is maintained here.
Con No 3-way merge
Cannot merge 3 files, can do only comparisons by pairs.
Makes it unsuitable for merging operations, still useful to compare two versions in the history.