The GNOME 2.23.x series are unstable versions, mainly intended for a series of tests for the stable version of GNOME 2.24. With the release of GNOME 2.23.6, the GNOME 2.24 code has also been frozen, meaning that all the new features appearing in GNOME 2.23.6 will basically be applied to GNOME 2.24. The next version, GNOME 2.23.90, is expected to be released on the 18th of this month. For more detailed information, you can visit the GNOME 2.23 development schedule.