Fallout 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.

Vault 13
Infinite XP received for completing the Water chip quest. Talk to the Water Merchants or keep the chip, travel to Necropolis and use it on the water computer there, resetting the water chip quest. Return the Water chip to the Overseer in Vault 13 again for 7500 more xp. Each trip between between the Hub and Vault 13 gains 8500 xp (and increases the time limit).

Shady Sands
Infinite Antidotes (each one takes four hours of Fallout-universe time): With only one Radscorpion tail in inventory, speak to the radscorpion expert, Razlo. "I have a sample of the radscorpion poison, can you do something with it?" When he replies, "Let me see the sac! Yes, I can do something with this", Barter the scorpion tail to him. You will receive the usual Antidote anyway. Antidotes sell for five times as much as tails, and nearly five times as much as it costs to buy the tails back. Note that he takes four hours to make them, and is only open from sometime after 6 AM to 7PM