KOReader is a lightweight, open-source document viewer primarily designed for e-ink devices, though it also runs on Android and other platforms. Its focus is on providing a highly customizable and efficient reading experience, supporting a wide range of formats including EPUB, MOBI, PDF, DjVu, and CBR/CBZ.

Developed with a minimal footprint, KOReader aims to offer superior performance and lower battery consumption compared to many commercial e-reader applications. Users can tweak numerous settings, from font rendering and margins to gesture controls and dictionary integration. The project emphasizes user control and a distraction-free environment for reading.

KOReader is known for its active community and ongoing development. Recent discussions on platforms like Hacker News, where it garnered 123 points and 43 comments, highlight its continued relevance and appeal among tech-savvy readers. The software is freely available under the GPLv3 license, encouraging contributions and modifications from its user base.