Recently Pyramid #3/115 Technomancer came out which updated some templates, added some backstory for whats been going on since it was published, and had articles to adapt it to the GURPS Action! and the GURPS Monster Hunters lines. See my review here.
So what is the setting all about?
Its earth just like ours, until the Atomic Bomb was tested. This unleashed magic into the world, though it took a second more powerful bomb for people to really start to understand what was unleashed on the world.
It uses modern technology mixed with the default GURPS Magic system but looked at with modern eyes. Industrial magic and mass production of enchanted items is a thing.
This makes for an easy to play modern fantasy world, just use real world maps in most cases.
Since things have come through the dimensional hole and magic warps living beings a lot of the standard critters exist, though twists like Atomic Liches and radioactive zombies add a scary change.