Avalonia is a cross-platform XAML-based UI framework providing a flexible styling system and supporting a wide range of Operating Systems such as Windows via .NET Framework and .NET Core, Linux via Xorg, macOS

Avalonia

CodeHub is an iOS application written using Xamarin

CodeHub

FlatBuffers: Memory Efficient Serialization Library

flatbuffers

CoreCLR is the runtime for .NET Core. It includes the garbage collector, JIT compiler, primitive data types and low-level classes.

coreclr

EF Core is a modern object-database mapper for .NET. It supports LINQ queries, change tracking, updates, and schema migrations.

efcore

If you want to keep a secret, you must also hide it from yourself.

shadowsocks-windows

.NET Decompiler with support for PDB generation, ReadyToRun, Metadata (&more) - cross-platform!

ILSpy

Google's Material Design in XAML & WPF, for C# & VB.Net. 

MaterialDesignInXamlToolkit

Microsoft Cognitive Toolkit (CNTK), an open source deep-learning toolkit