A well engineered template for creating plugins using object-oriented programming practices. Uses Settings API, multisite, i18n, PHPUnit tests.
Gives authors of new plugins a leg up on creating a great, easy to maintain plugin by providing a carefully designed plugin skeleton to build on. Authors of existing plugins can extract individual components and concepts for transplantation into their own projects.
See the FAQ section for more details about this plugin's features.
Development of this plugin template happens on GitHub. Please submit bug and feature requests, pull requests, wiki entries there. Releases are then squashed and pushed to WordPress' Plugins SVN repository. This division is necessary due having being chastised that "the Plugins SVN repository is a release system, not a development system."
If you want an explanation of how this "plugin" works, please see the "PHPUnit Tests for WordPress Plugins" series on my blog.