Boxes module is a reimplementation of the custom blocks (boxes) that the core block module provides. It is a proof of concept for what a re-worked block module could do.
The module assumes that custom blocks are configuration, and not content. This means that it is a reasonable action to ask for all blocks at one time, this is in fact exactly what the core block module does.
Boxes provides an inline interface for editing blocks, allowing you to change the contents of blocks without going to an admin page.
Boxes provides exportables for its blocks via the (required) Chaos tools module. This allows modules to provide blocks in code that can be overwritten in the UI.
Chaos tools is required to use Boxes.
The following modules provide Boxes plugins. Let us know if your plugin is not listed here.
Boxes provides a Spaces controller class that allows individual spaces to override a particular block, or even define a completely new block for a specific space.
Spaces is not required by boxes.
There is a screen cast that demonstrates the Spaces module integration here.