WinMerge is an 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.
Meld is a visual diff and merge tool. You can compare two or three files and edit them in place (diffs update dynamically). You can compare two or three folders and launch file comparisons. You can browse and view a working copy from popular version control systems such such as...
Beyond Compare allows you to compare files and folders. By using simple, powerful commands you can focus on the differences you're interested in and ignore those you're not. You can then merge the changes, synchronize your files, and generate reports for your records.
Diffinity is a diff and merging tool with focus on accurate and easy to read source code diffs. It will compare the content of two files and present the differences in an easy to read line by line and char by char basis.
Diffinity vs P4Merge opinions
Same look but easier to work with
Merge is the visual file comparison (diff), merging and folder synchronization application from Araxis. Use it to compare and merge source code, web pages, XML and other text files with native application performance.