WinMerge is Open Source, works for both files and flders and allows even comparing three files/folders.

Eu uso muito o WinMerge para revisar as alterações de código em arquivos grandes. O WinMerge tem suporte para até 3 janelas simultâneas de visualização ao mesmo tempo. Também podemos usar diferentes formatos de arquivos de entrada para visualizar e modificar o código. É realmente útil para aqueles que trabalham principalmente com arquivos de texto grandes para rastrear as alterações.

What I like best about WinMerge is that it provides the perfect set of features for my use case. I very often use the tool to view diffs between files of structured data such as XML or JSON, and it's moved block detection, highlighting of changes, and being able to ignore whitespace differences lets me visualize the important differences between two files. I like that it lets me do diffs on files, but also do diffs on any text I paste into the tool on the fly. But best of all is the price, as it is an open-source free-to-use diff and merge tool for Windows.