The following are complete games or supplements that are in the works (some of them on the verge of release, some still being playtested, and some still being written). This is in no way a complete list of what people in the OSR are doing; it merely includes the stuff I am personally aware of and interested in. However, if you think I left out something important, don't hesitate to put it in the comments.
Avatars & Annihilation
Van Noa's upcoming game; recognisably D&D-esque but introducing numerous changes to the subsystems, as well as to the game's aesthetics. A general pitch, many playtest reports, and numerous excerpts are available. I especially recommend the posts on starting equipment; a summary of HP, damage, and AC; and the spell list to get the basic idea.
The Complete Elementalist
Similar to his previous work, The Complete Vivimancer, Gavin Norman's upcoming supplement is going to detail a school of magic, probably along with appropriate magic items and monsters. According to the author, however, the meat of the writing is yet to be done.
Dolmenwood by Greg Gorgonmilk and Gavin Norman is an upcoming setting book inspired by weird folklore and fairy tales. Other than the general atmosphere, a map, and OSR compatibility, not much is currently known about the product's specifics.
The Final Castle
Brendan's upcoming game inspired by the tropes of JRPGs (in that regard, a spiritual successor to his own Gravity Sinister) and his experiences playing Dark Souls. The Final Castle is going to be "an integrated coupling of setting and rules", recognisable as a D&D variant (and thus being a good source of house rules) but a complete game on its own.
From the Vats
Gavin Norman ran a monster design contest in which participants needed to write up creations of vivimancers, statted for Labyrinth Lord. A compilation of these horrific creatures will be released titled From the Vats.
HMS Apollyon Player's Guide
Gus L is about to publish a Player's Guide to his own megadungen, the HMS Apollyon. So far a couple of excerpts have been made public (including reputation rules and the description of numerous factions aboard that cursed vessel).
Tom Fitzgerald has shared two sample pages of his upcoming "Middenmurk bestiary" on his blog (Dritherous Feorin and Grimmel-Dobbie), exemplifying how every single roll should have multiple consequences in order to gather the most information. For instance, a single roll determines not only "number appearing" but other details, as well, generating context and facts in a more economical fashion. So far we have only seen monsters but the final product may be much broader than a bestiary, especially if the first mock-up's page number is credible (that would make it one hell of a tome).
Courtney Campbell's upcoming game, Perdition, takes place in world conquered by devils. Its core gameplay should be very familiar to OSR gamers: there are perilous wildernesses, forgotten ruins, deadly dungeons, and hidden treasures. What makes it unique is how the subsystems are changed (skills, advancement, magic) and character options are tailored to the implied setting (meaning there are all new races, classes, spell lists, and more).
The Pernicious Atlas
Mateo Diaz has recently announced this supplement consolidating his creations for his Albion campaign in a single product. The supplement, as envisioned now, is going to include the description of 400 wilderness hexes, the Warlock and Beast Child classes, setting-appropriate spells and monsters, and tools running a campaign in New Londinium and its surroundings.
Kevin Crawford's upcoming game is a modern day occult-horror sandbox compatible with Sine Nomine Publishing's other titles. Not much is known about the game as of yet, only that it will feature a mythos creation system in which referees can generate their personal pantheon of Outer Gods and their cults who weave intricate plots against humanity, and tools to create alien races, forgotten and cursed places, and more.
Warriors of the Red Planet
A D&D-esque planetary romance adventure game by Al Krombach and Thomas Denmark. The game has its own blog and forum, and the beta version is currently available in paperback format from Lulu.
Wonders & Wickedness
Brendan proposed a spell level agnostic system in which every spell could be available to magic-users regardless of their level. Creating spell lists with this principle in mind resulted in the birth of Wonders & Wickedness, a tome of such level agnostic spells arranged by schools of magic, and also including some alternate rules regarding casters.
This grim and perilous RPG aims to produce an OGL and setting-agnostic dark fantasy "inspired by" first and second edition WFRP. It is currently in beta; the plan is to produce an art-free downloadable version, as well as an illustrated commercially available one (its specifics still undetermined).