The SharePoint Manager 2007 - http://www.codeplex.com/spm - is a SharePoint object model explorer. It enables you to browse every site on the local farm and view every property. It also enables you to change the properties (at your own risk). This is a very powerfull tool for developers that like to know what secrets the SharePoint holds.
SPContentTypeExplorer- http://spcontenttypeexplore.codeplex.com/ - This very small tool allows admins to find all the lists that are using a given content type. Rather than being stuck with a "This content type is still used...." when trying to delete one, you'll be now able to find where it is used.
SharePoint Designer Workflow Exporter - http://spdtoolkit.codeplex.com/ - exports workflows that are created using SharePoint designer to an feature. Making it possible to package in solution packages (WSP) See: http://agiledirect.wordpress.com/2008/09/10/packaging-and-re-using-sharepoint-designer-workflows-part-2/ or http://www.agiledirect.nl for more information.
WorkflowAssociationRepair - http://agiledirect.wordpress.com/2007/11/21/sharepoint-designer-workflow-association-stsadm-repair-command/ - TSADMCOMMAND that repairs this association by opening the configuration file, synchronizing version information and saving it back to the server, it also re-attaches the workflow using the WebPartPages webservice, which basically the same SOAP command when you are editing workflows in SPD and saving them. This tool comes in quite handy if you need restore loads of workflows on a site.
Windows SharePoint Services 3.0 Application Templates: All Templates - http://www.microsoft.com/downloads/details.aspx?FamilyID=5807b5ef-57a1-47cb-8666-78c1363f127d&displaylang=en -This download package includes all forty of the Application Templates for Windows SharePoint Services 3.0 plus the Application Template Core solution, which is required to deploy server admin templates.
SharePoint Solution Generator (VSeWSSv12) - http://www.microsoft.com/downloads/details.aspx?familyid=7BF65B28-06E2-4E87-9BAD-086E32185E68&displaylang=en - Windows SharePoint Services 3.0 Tools: Visual Studio 2008 Extensions, Version 1.2 – One of the extremely useful feature - generates a Site Definition project from an existing SharePoint site.
Stramit SharePoint Caml Viewer - http://spcamlviewer.codeplex.com/ - light view in SharePoint, convenient way to CAML querying
ULS Viewer - http://code.msdn.microsoft.com/ULSViewer - ULSViewer allows users to open a ULS log file and display its contents in a user friendly format.
SLAM! SharePoint List Association Manager- http://slam.codeplex.com/- In short it allows you to define relationships (one to one, one to many, many to many) between SharePoint lists (or Content Types) and then leverage those relationships in webparts or custom field types using familiar and straight forward SQL queries.
MOSS Manage User membership feature - http://mossusermembership.codeplex.com/ - This feature shows a new menu called "Manage User Membership" on site settings under "Users and Permissions" and permits to manage users membership. Extremlly usefull to view all groups to which specific user belongs.
Sharepoint SUSHI - http://www.codeplex.com/sushi -SUSHI = SharePoint Utility with a Smart, Helpful Interface. Tools which allows to run security report\bulk update\bulk site creation.
Windows SharePoint Services Software Development Kit (SDK)
Xavor SharePoint Admin Tool - SharePoint Admin tool is a web based tool that can give any site administrator "one click" access to a set of useful administrative tools (including Check access of any security principle (a user or a group) on any securable object inside SharePoint like SP Web, SP Site, SP List, SP list item). And more important it's FREE!
The latest finding - Microsoft SharePoint Administration Toolkit - the great tool to analyze SharePoint performance and also ships with check permissions tool which is handy in case you have a complicated permission logic with breaking inheritance
Sharepoint Space monitor - With this great application, administrators can now look at a Web Application and see what sites (and subsites and lists and libraries) are using the most space.
WssAnalyzeFeatures - to find the missing features with ease
A similar app - SharePoint Feature Administration and Clean Up Tool