DnSpy is a professional .NET decompiler, debugger, assembly editor and more.
Open a target .NET executable and the decompiler displays the results in a tree. References, resources, functions and forms are all expanded to readable code - even with some malware-like obfuscated assemblies - to help you figure out what the file is actually doing.
Right-clicking your assembly in the tree displays options to view it in a hex editor, or open its containing folder for further analysis. Or course there's a text search option, too.
If you know what you're doing then dnSpy can be used as a straightforward debugger. Set custom breakpoints, or tell dnSpy to break at some key starting events (CreateProcess, LoadModule, the first LoadClass, more), then launch the application and watch it work.
There's plenty more - including assembly editing - but beware, a total lack of documentation means you'll have to figure out the fine details all on your own.
DnSpy is a very powerful tool for inspecting and reworking the innards of .NET files.