“Ruby 1.9.3 p0 source code is made available under a 2-clause
BSD Licence and the Ruby Licence; previous versions of Ruby were
released under the GPLv2 and Ruby Licence. Other changes include
improved locking in multi-threaded programs, regular expression
support for Unicode 6.0 and a new library io/console for simple
portable access to the console. Also among the modifications are
changes to Random.rand and extra String methods such as prepend and
byteslice, though generally, the developers say you should be able
to safely switch to Ruby 1.93 from 1.9.2.”