Project Borealis is an attempt to flesh out the Half-Life 2: Episode 3 synopsis published by ex-Valve writer Marc Laidlaw in August into a full game, and an end-of-year update suggests that it's making good progress. According to a Reddit post from the development team, the story is around halfway complete and the AI, player movement and weapon functionality are now in place, albeit with a lot of testing still to do.

"The writing team has taken the initial Epistle 3 story posted by Marc and broken it down into critical plot points and then added more as needed to fill the gaps and flesh out a full and compelling story true to the lore and feel of the Half Life universe. Working through this more detailed story, the first 1/2 is nearly complete and undergoing review by the design teams," the team said.

The post contains a mixture of concept art and 3D models from the game, with a concept Arctic headcrab (above) and a fully completed Strider model (below) providing the highlights. If you want to dig into the details you'll also find 3D models for the iconic Gravity Gun and the meaty Spas-12 shotgun.

The team also released a couple of atmospheric music tracks that will make it into the final game and made a call for artist and level designers to get on board with the project. No word on when Project Borealis will be playable, but expect a huge fan-made project like this to take a while. The team wrapped up by promising more updates in 2018—I'll keep an eye out for any new tidbits.