dotPeek is a free .NET decompiler. While being a standalone tool, it is also part of ReSharper: If you tell ReSharper to navigate to the definition of a class
which is located in a .dll file, it will automatically decompile the file and present you the source code.
I don't want to use ReSharper. Can I get the same or a similar functionality without ReSharper or is this a ReSharper-only feature?
ILSpy
extension in VS 2019. It seems to work well and the ability to right click on a method name and inspect in ILSpy is very useful. It did take a minute for the context menu item to appear... possibly it was fetching debug assemblies? – Walleye