There's a lot going on in the world of open source software development, including some early looks at updates to several popular applications. Remember: beta versions of software are fun to play with and crucial for getting final versions out the door, but aren't stable enough for everyday use.
AbiWord 2.7.10 Beta - Open source word processor, AbiWord, mainly fixes bugs associated with plugins but there are also a handful of fixes for some cross-platform issues. You'll also want to check out this beta version if you've been having issues with importing and exporting Open Office XML docs.
Blender 2.49b - This is a full-blown point release of the powerful 3D modeling application that's so powerful some artists use it to create full-length animated films. In addition to fixing issues reported in earlier versions of the app, Blender 2.49b includes new features like projection painting, game engine speed-up, video texture, texture nodes, and more.
Audacity 1.3.9 Beta - Everybody's favorite open source, cross-platform audio editor and recorder is getting a minor facelift. This beta version of Audacity rolls out bug fixes for various issues like effects not loading properly, crashes while importing some non-MP3 files, and incorrectly disabled menu items. The Audacity team has two Google Summer of Code 2009 students to thank for all their help getting this beta version out the door.
VirtualBox 3.0.6 Beta1 - This popular free virtualization software lets you run multiple operating systems at the same time and is built to handle graphic-intensive games and apps. The latest beta version of VirtualBox is an early look at the next maintenance release that will fix a few niggling issues and add a few minor tweaks to help stabilize the app for everyday use.