2 generic game cheating tools and a disassembler
Cheat Engine is a free and open source memory scanner and editor, written mainly in Object Pascal (yeah, tough). It can be used quite easily to search for some in-game value (like ammunition count) and lock or edit it, for games that don’t encrypt or scramble what they put in memory. The provided tutorial is quite helpful to figure out how to do it. For games that try to protect themselves, this will be quite harder and I actually didn’t quite follow the provided tutorial about those. But if you study enough, it should be feasible as I’ve seen many trainers created with Cheat Engine.
Another great thing about it is that the community can share “cheat tables”, which are premade script or memory address lists that you can just load to cheat right away without diving yourself into memory analysis of your favorite games 🙂
CoSMOS is a close source equivalent published by CheatHappens. There might be a conflict of interests there, as CheatHappens provide non-free trainers to their subscribers. Still, CoSMOS is free to use and anyone can share their cheat scripts. However, in practice, the amount of freely available scripts seems low (quite a few are published in subscriber-only portions of the CheatHappens forums).
The greatest thing about CoSMOS in my opinion is the decent amount of pretty nice video tutorials to learn basic to expert use of the program. It should be moderately easy to follow these tutorials to learn to use Cheat Engine, as both programs are so similar.
OllyDbg is a free debugger, which I found mentioned in one of those CoSMOS video tutorial. It seems that some portions are open source, but sadly it also seems not to be very maintained as the latest update dates back to 2014… I guess time will tell. Meanwhile, it’s a nice debugger and it also comes with a disassembler.