From what I remember ALT.NET was pretty much a movement that was against Microsoft anti or ignorant OSS policies of the time.

For instance NuGet was Microsoft's project which completely ignored the fact that OpenWrap (an OSS project) had existed and was gaining momentum. But then NuGet came along and obviously the Microsoft loud speaker basically killed OpenWrap over night. That is just one example - but there are dozens of others.

ALT.NET was also about the social aspect, such as Twitter, meetups and non-Microsoft-owned .NET conferences.

I don't see the need for any kind of similar movement right now. Microsoft is firing on all cylinders and I believe it will only get stronger, wiser and bolder now.

It isn't long now before the .NET CLR will replace the JVM as the open source standard on which enterprise apps are built (and more) - watch this space!