It's a development version, because to be fully listed would require a stable release or one that gets updated there.
Since it is only a launcher that requires dropping Kovid's calibre-portable-installer-*.**.exe into the calibrePortable folder, both the first time and every time you want to update, that is difficult.
If you want to use the PortableApps version, google it, or search "calibre" on the PortableApps website.
Actually, I did it for you, so here you go:
http://portableapps.com/node/20518
Kovid's version should do just fine, but it won't have the same polish as a PortableApps.com package, like being autoplaced in a category, having a pretty popup when you select it in the PortableMenu, and of course it uses IMHO a superior way of dealing with remembering library locations.