Atlassian has just announced a SharePoint Connector for Confluence, their very popular wiki product (Atlassian also makes JIRA the issue tracking system).
Confluence is a Java based product, and SharePoint (MOSS 2007) already has wiki functionality included. So why am I, a Microsoft employee, highlighting this announcement? The wiki functionality in MOSS 2007 is great, but it's limited, and it doesn't meet the needs of all customers. Confluence is a mature popular product which some of my large enterprise customers are currently using. Those customers are also using MOSS 2007 and this product will let them bridge the two together into a single user interface with shared search provided by MOSS 2007.
I think this is a great example of the sort of Software + Services (S+S) integration that we are working to highlight with core parts of the Microsoft stack acting as the glue to tie enterprise applications from a variety of vendors together for improved user experience.
Here is a link to product information on the Atlassian site: http://www.atlassian.com/sharepoint/default.jsp