Decompiling

Hopper is a reverse engineering tool for OS X and Linux, that lets you disassemble, and decompile your 32/64bits Intel Mac, Linux, Windows and iOS executables!

OllyDbg is a 32-bit assembler level analysing debugger. Emphasis on binary code analysis makes it particularly useful in cases where source is unavailable.

Decompile Any .NET Code.

dnSpy is a debugger and .NET assembly editor. You can use it to edit and debug assemblies even if you don't have any source code available.

JustDecompile is a stand-alone, free decompiling tool which converts .NET assemblies into source code.

PEID is a signature scanner , it can detect most common packers, cryptors and compilers for PE files. It can currently detect more than 600 different signatures in PE files.