Decker is a multimedia platform for creating interactive documents featuring sound, images, hypertext, and scripted behavior, accessible directly in a web browser. It draws inspiration from HyperCard and classic Mac OS, aiming to replicate its ease of use while incorporating modern improvements like deep undo history, touchscreen support, and bulk editing.

Decker empowers users to create E-Zines, organize notes, give presentations, build games, or make pixel art, all within a cozy "ditherpunk" aesthetic that encourages a sketch-like, imperfect approach. Finished documents, called "decks," can be exported as standalone HTML files or run natively on Mac OS, Windows, BSD, and Linux.

For more advanced projects, Decker introduces "Lil," a novel scripting language influenced by Lua and Q. Lil is designed for ease of learning, offering features like implicit scalar-vector arithmetic and an integrated SQL-like query language. The platform also includes built-in widgets and supports custom widget creation and sharing via the clipboard. Decker is command-line friendly, with a headless interpreter called Lilt, and decks are stored in a text format compatible with source control tools.

Decker is free and open-source under an MIT license, with binary releases available on Itch.io. The platform hosts community forums and periodic "Game Jams," with the next upcoming jam being Decker Fantasy Camp in July 2026.