* Many new methods
* New socket API (enhanced IPv6 support)
* New encodings
* Random class that supports various random number generators
* Time is reimplemented. There is no longer the year 2038 problem.
* some regexp enhancements
* $: no longer includes the current directory.
* dl is reimplemented on top of libffi.
* new psych library that wraps libyaml. You can use the library instead of syck.