In the past Microsoft has been hostile to the open source movement
Microsoft has bolstered its credentials with advocates of open source software.
It has given cash to the Apache organisation which oversees development of open source web server software.
It has also pledged to open up some of its communications software and protocols so developers are free to study and use them.
The moves are seen as significant because of Microsoft's former opposition to the way open source software is written and maintained.
Cash and code
The announcements were made at the Open Source Convention in a keynote speech by Sam Ramji - a director of Microsoft's platform strategy.
Software written under an open source ethic gives its developers free access to the inner workings of the code.
By contrast the source code of the software produced by Microsoft is hidden and only available to a limited number of people.
In the past this difference has led Microsoft to criticise the open source movement and its development methods.
European Union regulators have battled for years to force Microsoft to release its Windows source code, and have fined the company more than 1.6 billion euros over the last five years for failing to make its software more interoperable with rivals.
In his speech Mr Ramji announced that Microsoft had become a platinum sponsor of the Apache Software Foundation. Microsoft did not disclose how much money it had contributed but becoming a platinum sponsor entails a donation of at least $100,000 (£50,000).
Many more web servers run using Apache software than use Microsoft's Internet Information Server (IIS). According to web monitoring firm Netcraft 49% of web servers run Apache compared to 35.9% for Microsoft's IIS.
The donation comes after Microsoft partnered with some developers at the Apache organisation on opening up its document formats.
In a blog posting explaining its decision Mr Ramji said the move should not be seen as it moving away from its own web server software.
Microsoft has also pledged to release details of some of its communication protocols under an open source promise. This lets developers use them for their own ends without fear of prosecution from Microsoft.
Finally, Microsoft has contributed a patch to an open source database project.