GNU Octave 3.8 hasn't been officially announced at the time of publishing, but the source package was uploaded just a short time ago to the project's GNU.org FTP server.
The big feature of Octave 3.8 is a graphical user-interface, which has long been requested by users of this open-source package looking towards it as a MATLAB alternative. While there's now a GUI, it's not yet polished now and will not become the default user-interface until the GNU Octave 4.0 release. GNU Octave 3.8 considers the GUI to be in a preview state.
Octave 3.8 also now uses OpenGL graphics by default in conjunction with FLTK widgets. GNUplot is still used in cases where OpenGL or FLTK support is not available for its graphical tool-kit.
Another change to GNU Octabe 3.8 is support for nested functions with scoping rules that are compatible with MATLAB, limited support for named exceptions, new regular expressions, a TeX parser for the FLTK tool-kit, overhauls to many of the m-files, function rewrites, and numerous other changes.
GNU Octave 3.8 also ships many bug-fixes and other improvements. While waiting on the official release announcement, more information on Octave can be learned from GNU.org.