Just found this on install.app. Builds off the original books.app but adds a nicer interface, autoscrolling, more document support and better speed.
From the website at colel.info/rubooks :
- FB2 support, including support to zip-archived files;
- Localization support, with English, Russian and draft German, Chinese and Japanese languages included;
- Text search;
- Page scrolling with volume control buttons;
- Increased book loading speed;
- Table of contents for single-file books;
- Book cover inside the text;
- Opening files anywhere on the file system under /var - including both home dirs of users "root" and "mobile". Also /var/root/Downloads;
- Color management for fore- and background in both day- and night-modes;
- Justified alignment and other small but very handy enhancements.