Accord.MachineLearning contains Support Vector Machines, Decision Trees, Naive Bayesian models, K-means, Gaussian Mixture models and general algorithms such as Ransac, Cross-validation and Grid-Search for machine-learning applications.
ORCHARD CMS is a free, open source, community-focused Content Management System built on the ASP.NET MVC platform
Cake (C# Make) is a cross platform build automation system with a C# DSL to do things like compiling code, copy files/folders, running unit tests, compress files and build NuGet packages.