The developers behind Ubuntu project announced Thursday the availability of version 9.04, codenamed Jaunty Jackalope. The new release ships with the latest desktop software and several new features.

The Ubuntu Linux distribution is developed around a six-month release cycle, which means that two new versions come out every year. The version numbers are based on the year and month of the release.

Ubuntu's launch schedule is based on that of the GNOME project—the open source desktop environment that provides the core applications and user interface in Ubuntu and other popular distributions. Ubuntu 9.04 comes with GNOME 2.26, which was released last month. The new version of GNOME includes a variety of incremental improvements, such as UPnP support for the Totem video player.

Jaunty ships with version 2.6.28 of the Linux kernel, the first kernel release in which the Ext4 filesystem is designated as stable. Ubuntu supports Ext4 and will allow users to choose it during the installation process, but Ext3 is still used by default because there are still a number of unresolved technical problems with the new filesystem. Ext4 offers better performance and boosts the maximum filesystem size to 1 exabyte.

Other applications bundled with the 9.04 release include OpenOffice.org 3.0 and GIMP 2.6.

One of the most significant user-visible changes in Ubuntu 9.04 is the introduction of Canonical's new notification system and messaging indicator applet. The old notification daemon has been replaced by a newer system that is designed to boost usability and aesthetic appeal. Users can now seamlessly click through notifications and interact with the windows below.

The messaging indicator is a new panel applet that aggregates persistent notifications from messaging applications across the desktop. The developers have already added support for its capabilities in Pidgin and Evolution. When a new e-mail or instant message is received, the messaging indicator icon will change and a notification item will be listed in the indicator menu. It can be used to keep track of incoming messages and quickly navigate to the relevant programs. The items in the indicator menu disappear when their respective applications gain focus.

I've implemented support for this feature in Gwibber, my open source microblogging program for Linux. Stay tuned next week for a detailed technical introduction to the messaging indicator with code examples that demonstrate how you can use it in your own programs.

Several other flavors of Ubuntu are also now available for download, including the server edition, Kubuntu, Xubuntu, and Ubuntu Studio. Kubuntu ships with KDE 4.2.2 and includes some improvements like the new KDE NetworkManager plasmoid, and several new programs, such as the Quassel IRC client. Xubuntu 9.04 comes with Xfce 4.6, which we reviewed last month.

Canonical has also announced an official release of the Ubuntu Netbook Remix, a custom version of the distro that is optimized for netbook devices. When the Netbook Remix was first introduced last year, it was primarily intended to be used for hardware makers who wanted to preinstall Ubuntu on netbooks. The 9.04 Netbook Remix release marks the first time that it has been made available officially as a user-installable image. It is supported on several off-the-shelf netbooks, including the Dell Mini 9, the Acer Aspire One, and several models of the Asus Eee PC.

Ubuntu is beginning to make considerable progress in the server space. The 9.04 release brings a few noteworthy improvements to the Ubuntu server edition that could help to further accelerate Ubuntu's growth on servers. It offers a first look at the Ubuntu Enterprise Cloud stack, which leverages the Eucalyptus project to to provide software infrastructure that will enable companies to build their own self-hosted computing clouds. Ubuntu 9.04 server edition is also officially supported on Amazon's EC2 service.

For more details about the release, you can refer to the official announcement on the Ubuntu mailing list. You can download the installation images from the Ubuntu website or via BitTorrent.