Workflow is one of the new core capabilities (along with WPF aka Avalon and WCF aka Indigo) being added in the .NET Framework 3.0 release later this year. It provides an in-process workflow engine to process rules, a designer for VS 2005 to enable both developers and non-developers to define custom workflow processes graphically, and a new Workflow namespace to integrate these within code. The official site to learn more about Windows Workflow Foundation can be found here.
Over the last two weeks I've also seen a number of great new posts and web-casts published that cover it in more detail. Below is a list of some of them you might want to explore to learn more:
Windows Workflow Foundation Basics:
.NET Rocks! Audio-Cast: Carl Franklin talks with Michael Stiefel about Windows Workflow Foundation and discusses what it is and why you might want to use. You can listen to this show here.
Bart De Smet has a number of great posts that cover some of the core concepts with Windows Workflow Foundation (WF):
K. Scott Allen has also posted several good blog posts on Workflow:
ASP.NET Page Flow:
ASP.NET developers should checkout the ASP.NET: An Overview of ASP.NET and Windows Workflow Foundation Integration web-cast that Kashif Alam from the ASP.NET team did earlier this month. It explores designing and developing UI workflow applications with ASP.NET and how developers will be able to use the new "Page Flow" capabilities that are being added to ASP.NET to enable developers to create representative UI for business processes defined with Windows Workflow Foundation (and avoid hardcoding in workflow logic in code).
For other great ASP.NET web-casts (both upcoming as well as past ones that have been recorded and published online), please check out this Web Casts listing page on the www.asp.net site.
SharePoint 2007 Custom Workflows:
SharePoint 2007 (which is coming out later this year and is built on ASP.NET 2.0) allows users to define and author workflows for common process activities. Sahil has a great blog post here that describes how to use this to define a custom process for a SharePoint site.
Hope this helps,