Firefox 3.5 is the fastest Firefox ever – check out this video of Director of Firefox, Mike Beltzner running through the new features. Please note, you can view the video without plug-ins using Firefox 3.5 and get a first-hand look at native audio/video support in the browser. You can download the Firefox 3.5 Release Candidate [...]

Release Candidate (RC) for Windows Vista and Windows Server 2008 Service Pack 2 are available for everyone to download.
You can download the Windows Vista and Windows Server 2008 Service Pack 2 RC from Customer Preview Program site or install through Windows Update using Windows Update Experience Kit.
If you have the SP2 for Windows Vista and Windows Server [...]

MySQL 5.1 RC is available for download. Few of the improments in MySQL 5.1 are listed

Advanced partitioning features
Events system
Row based replication
Table logs
New InnoDB auto-increment functionality

more here and download here