Fallout 2 exploits

Exploits are "holes" in the game programming which allow a player to do something which the developers did not intend and which alter the balance of the game in a way that benefits the player.

Broken Hills
Infinite XP: The Chosen One and at least one other party member, wearing Power Armor to protect themselves from the poisonous gas, enter the Mine. A wall on the right is found to immaterial and the Chosen One can pass through into a secret cave. The NPC ally is positioned to block off the exit, and the Chosen One approaches a sleeping figure in the cave. Asking him his name would normally gain 500 XP once, whereupon he flees, but with the ally blocking the way, the question can be repeated. Grab the nearby Uranium Ore for the next trick.

Infinite money: Infinite, but $1000 required at the start. With a Uranium sample in inventory, go see the glowing white ghoul technician at the uranium refinery. Pay him $1000, see him again a day later. Among the various options is one that pays $1500; this is repeatable.

Looting all the shopkeepers for free: When you enter Broken Hills Downtown, there is a wooden fence north of you. The edge of the fence does not cover the area between the edge of the map and the power plant control room completely; one hex on the edge of the map is accessible, and lets you walk on the other side of the fence. Go north-east until you find four footlockers. Three of these will contain the inventory of a shopkeeper; the fourth is used as a temporary storing place for a shopkeepers inventory during bartering - planting live explosives here and running to and bartering with a shopkeeper can be used as one of the weirdest assassination techniques in the game.

San Francisco
Infinite Karma: Format the Hubologists' hard drive for 25 Karma; repeatable under certain conditions. First: Ask Dave Handy in the Hubologist Base where he is from and why he came to S.F. Tell Hubologist Vikki that Dave likes her; tell him that she feels the same way. This last part closes off one option which gives extra XP when completing quest 10: "The tanker needs fuel", but allows the player to not only ask Dave handy to format the Hubologists' hard drive, but to do it repeatedly.

Navarro
Infinite XP and Power Armor, amongst other valuables: Go to Navarro, talk to Chris, and, after passing a speech check, you should persuade him into thinking you are an Enclave recruit. If successful, you will receive 1500 xp and will be able to give the gate guard the password. Then go to the quartermaster, tell him you're a recruit, then collect the loot from the adjacent room, which includes the power armor. If the player leaves Navarro and then returns, they can receive the xp again and the previously gained loot will respawn if the player passes Chris' speech check.

Modoc
Recruit Bess to Party:It's actually possible to have Bess join the Chosen One permanently throughout the game by means of an exploit. After she has been slaughtered by Grisham or after one has had the Bess encounter, return to a point in the game where Bess' broken leg has not yet been healed. This can be done by temporarily removing the file Modocmain.sav in the current savegame slot and replacing it with one that was made prior to healing Bess' broken leg. In this file variables regarding Modoc's main street are saved after visiting the area. When one now heals her leg again, she will follow the Chosen One for good instead of just in Modoc.

Before leaving Modoc, dialogue with her can also be initiated, allowing one to alter her combat options. After leaving town Bess stands in the spawn location for any map you enter...and not move...unless you save and reload, or when in combat mode, whereupon she will attack or follow at the distance set in combat options.

Though you can ask Miss Kitty to "hook up my friend here with a little something special" with only Bess in the party with you, dialogue just closes.

New Reno
Infinite Experience: Do Salvadore's line of quests. Before returning to get your last reward, use Mentants and wait until you drop to low intelligence. Attempting to talk to Salvadore will close the dialogue but still grant the 1000XP. This can be done endlessly and only requires 2 clicks.