This is a major redesign of sbt, so only prominent changes are listed:

 * New configuration system
 * New task engine
 * New multiple project support
 * More aggressive incremental recompilation for both Java and Scala sources
 * Merged plugins and processors into improved plugins system
 * Web application and webstart support moved to plugins instead of core features
 * Fixed all of the issues in (Google Code) issue #44
 * Managed dependencies automatically updated when configuration changes
 * `update-sbt-classifiers` and `update-classifiers` tasks for resolving sources and/or javadocs for dependencies, transitively
 * Improved artifact handling and configuration
 * Tab completion parser combinators for commands and input tasks
 * Project definitions are in Scala 2.8.1

Note that the project has completely moved to GitHub now: <https://github.com/harrah/xsbt>

Documentation may be found at <https://github.com/harrah/xsbt/wiki>