Hannes Magnusson, in an effort to make it easier for developers to play with the latest shiny features of the current PHP development, has created a PPA for the latest daily status of the PHP project's trunk line of code.
There is still no public "development preview" or alpha release, but that doesn't mean we can't play around with it, report bugs, ensuring our apps still properly work with it etc etc etc. It is however a bit annoying needing to "go old-school" and fetch a snapshot and build it yourself though.
If you'd like to try it out for yourself (the generated Ubuntu packages), you can get more information over on the Launchpad page for the project. As always, feedback is welcome on the PHP internals list about your experiences.