I've worked on Collapsiblock previously on Drupal 6 and didn't like how the whole thing worked. While it gets the job done, I needed to refactor a few things to make it better.
Now I'm starting a new project on D7 and I need this module again. I've refactored the code make it easier to read, style and theme.
Additionally my module does more logic on the server side instead of on the javascript side. I do this because I don't want the end users to see the blocks collapsing after the page loads, a problem I have currently with the available version. My version will output .collapsiblock-collapsed into blocks which should be collapsed by default, which you can use to style collapsed in your theme. This CSS is already included though.
For blocks where the users have chosen them to be in a different state than the default (via saved cookies), one of the first things this module does is toggle the .collapsiblock-collapsed to the users desired state, reducing the effect of watching blocks get show, or closed on page load.
This sandbox will be presented to the maintainer of collapsiblock and with any luck he'll accept it and it'll become collapsiblock v2.
PS. There are still some bugs related to default state. Should work fine if your default state is none.
