Moving some planks of wood I came across a few of one of our interesting spiders, which is very flat an black, but actually is call a Flattened Sac Spider, one of some 180+ described species of Australian Sac Spiders. These spiders get their name from their habit of building silken sac retreats and egg sac.
The Flattened Sac Spiders are in the Family Gnaphosidae and I think this one is in the Genera Rebilus and is atypical in that it does not build a silken retreat but does have very flat disc sacs for its eggs.
These spiders move extremely fast and I was lucky to have this one stay still long enough for a photo. Their speed is used in hunting prey as they run them down and strike before the prey is even aware of their presence.