Cobalt is an open-source application platform for Kobo e-readers: a launcher, a signed App Store, a Rust SDK, and a runtime that keeps every app in its own unprivileged process.
Install it once over USB. Every app after that installs, updates and removes on the reader itself, over Wi-Fi. A reboot returns to the stock Kobo reader.
Every app is a static ARM binary running as its own unprivileged process on stock hardware. The App Store installs, updates and removes them over Wi-Fi, with signatures verified before anything launches.
These are photographs of the device, not simulator captures. The arXiv app reads the HTML rendering arXiv publishes for every paper since December 2023: abstracts, sections, math and result tables, paginated for the panel.
Every screenshot below is a capture from a Kobo Clara BW. Store apps version independently of the platform; the rest ship with the platform install.
Opens installed apps and always keeps a route back to the Kobo reader.
Installs, updates, removes and reinstalls signed apps over Wi-Fi.
Browses a subject’s newest preprints and reads the full text on the panel.
Store-only by design: installing it proves delivery of an app the USB package never contained.
Sends a typed message in Morse on the front light, one letter across the whole panel.
Researches, writes, narrates and plays an original audiobook.
Reads any OPDS library: Project Gutenberg, Standard Ebooks, Open Library, or yours.