[Transfer: http://www.cnblogs.com/itech/archive/2009/08/13/1545344.html]
Summary of free and easy-to-use Diff and Merge tools
Summary: Compare: diffmerge and P4merge are the best, kdiff is more professional and supports automatic merge.
a csdiff
Download: http://www.componentsoftware.com/Products/CSDiff/index.htm
Features: 1) Free; 2) Installation required; 3) File and folder comparison; 4) Source code, html and word documents supported;
screenshot:
1) Initial interface
2) folder comparison
3) File comparison
two diffmerge
Download: http://sourcegear.com/diffmerge/
Features: 1) Free; 2) No installation required; 3) File comparison; 4) Support 3-party file comparison and merge; 5) Windows shell integration; 6) Cross-platform;
screenshot:
1) Initial interface
2) folder comparison
3) 2 files compare and merge
4) 3 files to compare and merge
and 
三 P4 Diff and merge
Download: http://www.perforce.com/perforce/products/merge.html
Features: 1) Free; 2) Need to install; 3) File comparison; 4) Support 3-party file comparison and merge; 5) Cross-platform;
screenshot:
1） p4diff
and 
2） p4 works
and 
four kdiffs
Download: http://sourceforge.net/projects/kdiff3/
Features: 1) Free; 2) Installation required; 3) File comparison and folder comparison; 4) Support 3-party file comparison and merge; 5) Cross-platform; 6) Automatic merge
screenshot:
1) Initial interface
2) Folder comparison
3) File comparison and merge
Five Totorise Merge
Download: http://tortoisesvn.net/downloads
Features: 1) Free; 2) Need to install; 3) File comparison; 4) Support 3-party file comparison and merge;
screenshot:
1) Initial interface
2) File comparison and merge
六 Winmerge
Download: http://winmerge.org/
特点：1）免费；2）需要安装；3）文件比较和文件夹比较；4）支持merge；5）Shell集成
截图：
1）初始界面：
2）folder比较
3)文件比较
七 命令行diff
对于命行的diff，在Linux可以使用diff.exe，在windows可以使用fc，comp和来自Linux的diff.exe。
八Linux diff和merge工具
Meld ：http://meld.sourceforge.net/index.html
九Araxis Merge很好的文件夹比较工具