dnSpy is a .NET assembly editor, decompiler, and debugger forked from ILSpy.
dnSpy was created by 0xd4d, the same guy who made de4dot, the popular .NET deobfuscator.

Features
Assembly editor
Decompiler
Debugger
Tabs and tab groups
Themes (blue, dark, light and high contrast)

Github Link: https://github.com/0xd4d/dnSpy
Releases (Downloads) Link: https://github.com/0xd4d/dnSpy/releases

Preview: