Stéphane Graber was the one announcing the Raring Ringtail 13.04 Alpha 1 release this time around. Due to changes to the release schedule, there isn't the usual Ubuntu Linux alpha releases like in past cycles. The first official Ubuntu 13.04 development release will be a beta at the end of March. Those wanting to test upstream Ubuntu are just encouraged to use the daily Ubuntu Linux images that are usually in good shape.
As for what's actually being released today, the mailing list announcement notes the releases of Edubuntu 13.04 Alpha 1 and Kubuntu 13.04 Alpha 1. Download information and other release details for the Linux images being tagged as 13.04 Alpha 1 can be found from the ubuntu-devel-announce list.
Among the changes happening for Ubuntu 13.04 are Ubuntu TV improvements, X.Org and Wayland updates, hybrid graphics improvements, 64-bit ARM support, integration of the Linux 3.8 kernel, strides towars having an Ubuntu SDK, Unity performance improvements, gaming enhancements, and a whole lot more.