Invaluable software

Not all these recommendations may be needed for you, but if the software is relevant to your field, you simply should have them installed.

7-zip

Free general-purpose archiving software that can handle a lot of formats.

UPX

UPX is a free, portable, extendable, high-performance executable packer for several executable formats.

Dependency Walker

Dependency Walker is an incredibly useful tool that allows you to open an executable or DLL and see exactly what DLLs it depends on, what functions they expose and which are used.

Path Editor

This rather obscure tool is great to quickly edit your PATH in a visual way.