Check the "Download" link on the left side of the page. This leads to
https://github.com/koreader/koreader/wiki/Download which in turn gives two options; Nightly Builds -->
https://github.com/koreader/koreader/releases and Stable Release -->
https://github.com/koreader/koreader...2014.04-stable
As to which one you want I have no idea.