Parrot: Revision 4
Parrot is the VM (virtual machine) that the Rakudo Perl 6 compiler is built on, just as Pugs is built on Haskell (although Pugs can also emit code for Parrot).
Parrot is the VM (a software cpu) that was originally designed for Perl 6, but which is also intended to be a generally dynamic-language-friendly platform for Python, Ruby, and many other languages.
Parrot exists because other VMs (like the JVM and CLR) did't (and mostly still don't) have strong (and efficient) support for 100% of the super-dynamic language features of Perl 6. And while support for these features has improved in the past few years, leading to projects like IronPython, these VMs are still primarily designed for (biased towards) static languages.
Parrot also incorporates a number of other important and noteworthy innovations (for example, it's a register-based virtual machine). See the Official Parrot Wiki for the full details and latest developments.