In 2012, Valve's Gabe Newell mentioned a canceled game called Stars of Blood, saying only that, "We kind of had an internal project that was called Stars of Blood, which was a space pirate game and it never saw the light of day." Concept art by a couple of ex-Valve artists had previously leaked, and more was unearthed later—some from photos taken on tours of the studio. The fans at Valve Archive put together a repository of Stars of Blood art, where it's been sitting ever since.
Over the weekend, the Obscure Game Aesthetics Twitter account, which posts screenshots and artwork from old or forgotten videogames, posted four concepts for environments from Stars of Blood. It followed with a tech demo of swarm AI from one of the ex-Valve employees who worked on Stars of Blood, theorizing that this too might be from the canceled game. It's since been posted to r/LeaksAndRumors, r/GamingLeaksAndRumours, r/pcgaming, r/Games, r/GamePreservationists, and r/UnreleasedGames, as well as doing the rounds of various websites, forums, and social media.
The character designs are a bit Moebius (there's even one called mumbiusSM.jpg), and rumor had it that Stars of Blood would involve the Combine, and be part of the Half-Life universe. Not much else about it was known, but "Valve space pirate game" is all you really need to be intrigued. Now it's just another game that will never be, alongside the various Half-Life projects that were canceled before Alyx, Arkane's spin-off Ravenholm, Prospero, and all the rest.