HashTab provides OS extensions to calculate file hashes. HashTab supports many hash algorithms such as MD5, SHA1, SHA2, RipeMD, HAVAL and Whirlpool. Hashtab is supported as a Windows shell extension and a Mac Finder plugin. HashTab provides an easy way to verify file integrity and authenticity.
HashTab is a Windows shell extension which adds a tab called "File Hashes" to the Windows Explorer file properties. The tab contains the MD5, SHA1 and CRC-32 file hashes by default, but can be configured to support a number of other popular hashes. The HashTab makes it very simple for Windows users to check these hashes on any file on the system without using external tools. The screenshot below shows an example.

What are hashes good for?
A hash of a file is a "signature" generated using a cryptographic algorithm. Many download sites provide a .md5sum file along with along with the download link. The contents of the .md5sum is the signature of the file. If a single bit in the download changes (becomes corrupted during transfer to your system) the "signature" will change dramatically. The purpose of HashTab is to make it as simple as possible to validate these file "signatures" thereby allowing you to know that the file you asked for is exactly the file that you received.

The license of this software is Freeware, you can free download and free use this shell extension software.