WF allows you to create workflows of activities. We have been careful to make WF very extensible - including writing custom activities (e.g.MySendMail activity) and entire libraries of activities. I just came across my first example of a complete library which today is available in Beta and works with the February CTP of WinFX.

It includes Internet activities for File Transfer (FTP, TFTP, etc.), Sending and Receiving Email (SMTP, POP, IMAP, etc.), Web and Web Services (HTTP, SOAP, RSS, etc.),  Network Management (SNMP, DNS, Ping, etc.), and Instant Messaging (Jabber, SMS, etc.). 

You can find out more from http://www.nsoftware.com/workflow/ and download the library from http://www.nsoftware.com/download/beta.aspx 

Which leads me nicely to... do you have a product with functionality that would make sense to expose as an Activity Library for WF? Yes, maybe? Have a think... I bet you have :-)