How do I use them? - Save your current game. Backup your original /data/main.scm by renaming it to something like mainORIGINAL.scm. Put the SCM file from the ZIP you download into its place and make sure you rename it to main.scm like the original was. Load your game and most Code Tools will begin automatically. If it's a Code Tool that changes something about the game, save your game. Now replace your main.scm with the original one, load the save you just made, and continue playing as you normally would.
What makes Code Tools so special? - First and foremost, because they are designed to work with your existing game, something previously thought next to impossible and/or worthless. Also, there are SOME things that trainers aren't made to do that some of the tools can.
Ancestral Recall - How often do we see somebody asking what they might have left? Well GTA3 is capable of sealing missions, so nobody could ever answer this... until now. With Ancestral Recall, you'll know exactly what you have left to do to get 100%! To install Ancestral, you will additionally need to backup and replace your /TEXT/american.gxt like you did with your main.scm. When you load your game, you will hear 3 chimes letting you know the mod has started. It will continue to display everything you have left to do. When it's done scrolling through (or if you die or get arrested), it will chime 3 times and do it over again. When you've seen all you need to, replace your /data/main.scm with the one you backed up before, load your game again, and go do what you need to. Note: Ancestral Recall WILL alert you that you need to do Paramedic if you have not yet received hideout Health or Adrenaline. It will NOT alert you that you need to do Paramedic if you have those, but do not have infinite run. Either run and get tired or see a Paramedic level completed lower than 12 in your stats to know this. Missions that you have not yet passed and are sealed and can never be passed will appear in red instead of the usual white. You can use the Eureka Code Tool to credit you for those. Also, the american.gxt that comes with Ancestral Recall is the original game, plus the keys you need for AR as well as my Coordinator mod. So you can just leave it there if you'ld like.