There was recently an interesting exchange of emails on the Drools user mailing list about running Drools Expert on Android, which has been the Holy Grail of some users for some time.
One particularly active community member on this front, Abhay Chaware, blogs about their experiences, tricks and tips here.
Unfortunately Abhay was unable to solve the final hurdle as the blog reveals, however let Abhay's research spur other talented community members to attempt the same and hopefully close the last(?) issue.
As the title of Abhay's blog suggests "At least I tried".