Microsoft Exchange alternatives

Microsoft Vows to Fix 'Broken' Code In Open Source...
Cloudline: "Microsoft says it is committed to making good on its OpenStack promises just as it did with Hyper-V and Linux."

Microsoft Azure gets an open source rival
InfoWorld: "Tier 3 is providing a cloud alternative for Microsoft .Net applications."

Can an open-source backer thrive inside Microsoft?...
All About Microsoft Blog: "I realize every story has two sides. For what it's worth, here's Verissimo's side of his tale about his three years in Redmond."