Cheat Engine is an open source tool designed to help you with
modifying single player games running under window
so you can make them
harder or easier depending on your preference(e.g: Find that 100hp is
too easy, try playing a game with a max of 1 HP), but also contains
other usefull tools to help debugging games and even normal
applications.
It comes with a memory scanner to quickly scan for variables used
within a game and allow you to change them, but it also comes with a
debugger, disassembler, assembler, speed hack, trainer maker, direct 3D
manipulation tools, system inspection tools and more.
Download: