Pretzelfisch

.NET DiscUtils
.NET JSON parser & deserializer
.NET Transactional File Manager
.NET Zen Linq Extensions
51Degrees.mobi - Mobile Device Detection and Redirection
A Fast Expression-Based Enhancement for Reflection
A Rich Full Featured WPF/SL MVVM Framework
Abidar
Aimee.net - Refactoring Lucene.NET
Albatross
Algorithmia
AlphaFS - Bringing Advanced Windows Filesystem Support to .NET
Alter gear SQL index Management
ASP.NET
ASP.NET MVC / Web API / Web Pages
AutoMapper
AvalonDock
Azure Publish-Subscribe
AzureKit
Base Class Libraries