This also works nicely for Jad/fight kiln. Get to jad in real runescape and then login to beta.
It's been around since 2012. Works on any boss (as long as no one else is killing it). You can also get free stuff in beta but this is not about that, it's about not needing to rebank and waste your own resources.
Combat beta (for F2P too!):
(LINK DELETED, DOES NOT WORK ANYMORE)
EVERYTHING THAT YOU DO IN BETA WILL NOT BE SAVED. ALL DATA WILL BE DELETED IN A FEW WEEKS. BETA IS FOR TESTING PURPOSES ONLY.