Output's Kontakt/Player library, REV, is based on a library of reversed sounds and comprising four instrument "engines" - each one powering a sizeable collection of categorised presets.
Instruments are keyboard-playable multisampled patches; Timed Instruments are timestretched instruments; Loops are banks of tempo-synced, pitchable loops; and Rises are various types of timed build and riser.
Each engine has its own interface (they share many common controls). Instruments and Timed Instruments are dual-layered, with four versions of each sample (reverbed, dry, looped and forwards), enabling you to mix and match.
The engines aren't dazzlingly innovative, but Output has used many of Kontakt's best scripting features, like triggerable effects and timestretching, to great effect. The main thing is that it's a 6.8GB sample library that's beautifully produced and endlessly explorable.