Cheat Engine :
Cheat Engine is a tool designed to help you with modifying single player games without internet connection 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, and helps you protect your system by letting you inspect memory modifications by backdoors and even contains some ways to unhide them from conventional means.
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, speedhack, trainer maker, direct 3D manipulation tools, system inspection tools and more which are also useful for normal programmers and software analysts.
Besides these tools it also comes with extensive scripting support which will allow experienced developers to create their own applications with ease and share them with other people.
System Requirements: Windows 7 and later