It's first major update for a long time since previous version.
Changes in this beta
New much improved modern user interface
Support for multi-user environments
Much better image quality for layers in Mercator projection
Improved Layer Manager - quick layer settings, drag'n'drop layer reordering, save/restore current config
List of all features planned for 0.9.88 and more info is available at http://ww2d.csoft.net/index.php?title=Version_0.99.88