We use Microsoft for everything but I'm hoping to cut the costs here in the office by switching things to open source.....or more importantly, free.

Right now we use Microsoft Office, I'm already bringing up Open Office as an alternative but does it have the same capabilities as an Exchange server and a Blackberry Enterprise Server (BES)?

We also use ArcGIS as a mapping application but I'm wondering if there are many more free but powerful mapping tools out there. We don't use everything ArcGIS has and the licenses are about $10,000 which we charge our clients for.

Also our servers are running IIS, I'm attempting to get over to Linux, especially since we run Oracle which is made more for it.

And we develop primarily in .NET so for an environment we use Visual Studio along with Visual Sourcesafe for code organization and version control. Is there any combination that will work as well as these but are free? We also do a little bit of VB6 and C# work but not much.