This describes it better then I could

"The Sysinternals web site was created in 1996 by Mark Russinovich and Bryce Cogswell to host their advanced system utilities and technical information. Microsoft acquired Sysinternals in July, 2006. Whether you’re an IT Pro or a developer, you’ll find Sysinternals utilities to help you manage, troubleshoot and diagnose your Windows systems and applications. If you have a question about a tool or how to use them, please visit the Sysinternals Forum for answers and help from other users

and our moderators. " – http://technet.microsoft.com/en-us/sysinternals/default.aspx

 

Sysinternals Utilities Index

Sysinternals Suite
The entire set of Sysinternals Utilities rolled up into a single download.

AccessChk
v4.23 (December 19, 2008)
This update fixes a bug that sometimes caused AccessChk to not show the full list of rights and privileged assigned to a user account.

AccessEnum
1.32 (November 1, 2006)
This simple yet powerful security tool shows you who has what access to directories, files and Registry keys on your systems. Use it to find holes in your permissions.

AdExplorer
v1.01 (November 27, 2007)
Active Directory Explorer is an advanced Active Directory (AD) viewer and editor.

AdInsight
v1.01 (November 20, 2007)
An LDAP (Light-weight Directory Access Protocol) real-time monitoring tool aimed at troubleshooting Active Directory client applications.
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