Is there an official roadmap or product backlog anywhere?

Is there an official roadmap or product backlog anywhere? I am interested in contributing, possibly to the viewer.

I was looking at the following: [Plugins for Viewer (to allow RSVP) - MobileRead Forums](https://www.mobileread.com/forums/sh...d.php?t=342645), because I was interested in making some viewer plugins (not possible ATM). It mentions that viewer plugins are on the TODO, but this seems like a more informal TODO.

Thanks! And thanks for all your awesome contributions! Calibre is a really cool project!