Star Wars Age of Rebellion Cyphers and Masks is interesting in that there have been few past Star Wars RPG resources devoted to spies and espionage. Infiltration and working behind enemy lines is obviously a major element in Rebel era games and touched on often in all kinds of sourcebooks. WEG's various Cracken's books were intelligence oriented, some with gear, though most concentrated more on providing NPC adversaries and some adventure ideas. Cyphers and Masks is the first to really pull together in one place, everything from character options to spy gear to campaign ideas, to new ways to use the narrative dice with skill checks.
My contribution to Cyphers and Masks is the Spy Backgrounds and Spy Campaigns sections. The Spy Backgrounds section gives players (and GMs) ideas as to what job or lifestyle helped them to become effective agents. Things like freerunners, law enforcement, performer, and a few other unusual but interesting options. The three campaigns gives the GM ideas and outlines different elements of espionage stories: one focuses on a single target, one sets up a larger scale sleeper cell operation on the planet Duro, and the third puts the PCs in the heart of a complex diversion of Imperial goods to Rebels, right under the Imperial's noses.
The Covert Ops section is one of the most interesting, and useful beyond just espionage adventures. The section presents new ways to use certain skills and recommendations for spending narrative dice icons (advantage, despair, etc.). Computers, Deception, Skulduggery, and Stealth are all covered.