The new version of Base adds new classes for NSPredicate, better url management (implementing the last api additions from apple), as well as improving support on Windows.
On the GUI side, among the noteworthy changes since the previous release (0.10.3, march 2006) is the new support for key encoding in all gui classes — which means you can now load and save OS X nib files.
Some explanations: with GNUstep and Cocoa, your interface is created using a graphical tool (IB on OS X, GORM on GNUstep) and stored in a "nib file". The nib file format used to be proprietary, which is why GNUstep had to use its own, portable format. Apple switched to a xml key-encoding format in recent version of OS X, which let GNUstep implement load/save support for it.
What it means is that you can now take your Cocoa program and simply recompile it on GNUstep, without needing to recreate the UI in GORM. Conversely, you can take your GNUstep program and recompile it directly on OS X, without recreating the UI in InterfaceBuilder.
In addition to that, the usual bugfixes and improvement on many classes (NSWorkspace, GSSystemManager, NSHelpManager, NSTableView, NSToolbar, etc.), RTFD support, some work improving the color scheme and theme support, better GDI support with the Windows backend, better Cairo backend, etc."