There are many modal window plugins, commonly known as “lightbox”, available online: multiBox coded by phatfusion is powerful and relatively lightweight, it is probably the best option within the MooTools framework.
Starting from that script, Manfred Rutschmann, has released the WordPress Multibox Plugin, to make the installation process into a WordPress blog easy and straightforward.
Unfortunately, this plugin could conflict with other extensions, since it injects <script> tags into the page without checking if the code has already been loaded, as the WordPress documentation crearly recommends.
Scripts developed under the MooTools framework are useful to easily achieve complex menu displaying effects.
For instance MooTabs creates tabbed menu, like those used by the browser or the OS, from ordered and unordered lists. This could be a great option if dealing with small spaces in the page: when clicking one of the triggers, the content of the main box gets replaced, with custom styles and transitions.
The script class, originally built for earlier MooTools 1.11, has been completely upgraded in Fx.Tabs for the newest framework version, while Perspective Tabs offers an even more complex approach.
Similarly, MGFX.Tabs is driven to the same purpose, by crossfading the CSS opacity value instead of sliding the content.