Thieves Arsenal, by Paul Connelly, is a mod for The Elder Scrolls IV: Oblivion and Oblivion Scripting Extender (OBSE).
The mod adds Thief-like tools and weapons to the game. The new weapons include Blackjack, Water Arrows (which can also be blessed with holy water to deal damage to the undead), Vine Arrows (which can be replaced with Rope Arrows through customisation, as the functionality is identical), Noisemaker Arrows, Gas Arrows and Grease Arrows.
The mod also features changes to the AI so that NPCs can be knocked out using the blackjack, will react to player using these weapons, and to react to unconscious or dead characters. Also, all torches in dungeons and castles have been made extinguishable with Water Arrows. Finally, the mod features Basso the Boxman who has a hidden shop in the Imperial City - you can purchase this equipment from him, and receive randomly generated "odd jobs" from him.