Trilby: The Art of Theft
From the author's description:
"The game's called Art Of Theft. The long version is Trilby: The Art Of Theft, because it features everyone's favourite dapper renegade from the Chzo Mythos (I stress that it's set in 1991, two years before 5DAS, so don't think it's a continuation or anything).
AoT isn't an adventure game, though. It's a mission-based stealth platformer using a severely modified 1213 engine, with the emphasis on gameplay rather than story. As a younger, more arrogant, more complacent Trilby your goal is to infiltrate a variety of buildings in the fictional Chapow City, steal loot, achieve objectives and get out again with the subtlety of a flickering shadow in a ninja outfit."
An excellent and detailed Walkthrough by Radiant (Local mirror, 2nd January '08). Details all the skills and recommended purchase order, the costumes and how to get them, and how to approach each level.
A full video walkthrough by Terry Cavanagh is available on TIGSource (Local mirror, 2nd January '08). Shows a Trilby Rank playthrough of each level and each level's mission text, as well as all the cutscenes. Doesn't include the bonus heist.