FreeFileSync

FreeFileSync is an Open-Source folder comparison and synchronization tool. It is optimized for highest performance and usability without restricted or overloaded UI interfaces. It supports comparison by date or content, filters, file sizes > 4GB, delete-before-copy for large sync operations, and creation of batch files for automated synchronization.

FreeFileSync has a myriad of options for syncing files between two folders and locations. The user interface is especially user friendly and makes it easy to quickly adjust your settings.

Whether you need to simply compare folders and update the files to the newest version or you want to create batch files for recurrent comparisons, FreeFileSync has you covered. If you have multiple locations to compare, you’ve saved a document to My Documents, on a flash drive, and have an emailed copy of it you just downloaded, FreeFileSync can compare all three versions easily.

You can specify whether you want file comparison to be based on size and date or you can have it do an actual comparison of the file. You can quickly switch between simply comparing and actually syncing the files; when you’re ready to sync, the central column between the two comparison panes allows you to rapidly choose which file will get synced in which direction or which files should be temporarily ignored by the syncing process.

If you’re not tweaking things manually with the center column you can sync everything bit for bit with a mirror sync, use the two-way sync to copy the new files from each folder to the other folder, and the update sync where only the new and updated files will be copied.

FreeFileSync is freeware, Windows only.

http://freefilesync.com/

FreeFileSync是一款使用简单的开放源码文件夹同步和比较软件，它用于快速简便的配置和行动之间的同步两个文件夹。

FreeFileSync 首先是文件同步功能，可以在指定的两个文件夹之间进行单向或双向的同步，点击程序窗口右上方的绿色齿轮图标可以设置相关参数；期间也可以自定义需要筛选的文件，有“包括”和“例外”两种过滤方式，定义需要过滤的文件类型，这就看个人需要了。
此外就是比较不同文件夹中的文件是否相同的功能，不过这个功能比较适合同步之前使用，比较的结果会直接显示在列表中，方便查看，这样你就可以清楚的知道是否需要进行同步操作了，节省系统资源。