DayZ Origins is an unofficial spin-off of Arma 2's now famous zombie survival gametype - a mod of a mod, if you will. It took some flack over using the DayZ name, but its creativity's been praised by DayZ's creator Dean "Rocket" Hall. And given the substantial ambition evident in its latest update, it's not hard to see why.
Origins 1.0 introduced a survivor city where the moneyed elite had holed up, protected by high walls and mercenaries. It created a shared objective for players, who could band together to fight their way in. 1.5 sees the city's occupants fight back, sending sorties of mercenaries to the mainland, making survivors' plight all the more perilous. It also introduces Mad Max-style jury-rigged vehicles - entirely customisable by players. You can jam a plough onto the front of a truck to hoof dead-heads off the road, or even add wheels to a boat to make an amphibious vehicle. There are player-made encampments, too, which can be upgraded over time.
There are a dozen new zombie types, too, each with different capabilities, and a large number of additional locations built onto a modified version of the Tavania map, including a race course and safari park - plenty of stuff to keep zompocaylpse survivors busy while awaiting the official standalone version of DayZ.
Head over to www.dayzorigins.com for the full feature list. The client files should be uploaded and ready for download imminently.