A free online malware analysis tool. It runs the EXE in a isolated virtual machine (sandbox) and generates a report detailing exactly what files the EXE tried to modify, what registry keys it touched, and what websites it tried to contact. Step-by-Step: How to Decompile an EXE File

: A free standalone tool from JetBrains that decompiles .NET assemblies into equivalent C# or IL code.

Comprehensive analysis. It shows you multiple decompiler outputs side-by-side so you can compare results. 2. RetDec (Retargetable Decompiler)