SharePoint Foundation 2010 is the next version of Windows SharePoint Services. Formerly known as Windows SharePoint Services 4.0, SharePoint Foundation 2010 provides essential solutions for organizations to do secure, manageable and web-based collaboration. Best of all, it's technically free.
With the availability of 64-bit hardware, SharePoint Foundation 2010 (including the full-blown SharePoint Server 2010) now requires the 64-bit version of Windows Server 2008.
* Windows Server 2008 Service Pack 2 for non-R2 systems
* Web Server Role (IIS 7)
* Windows PowerShell 2.0 for non-R2 systems (Windows PowerShell 2.0 ships with Windows Server 2008 R2 and Windows 7 so you no longer have to worry about that)
* .NET Framework 3.5 with Service Pack 1 (in R2 systems, this can be enabled via the Add Roles Wizard)
* Windows Server 2008 hotfix for token authentication (non-R2 and R2 systems)