The listings were uncovered through the Steam Apps Database, a public version of the database that underlies Valve's Steam client and recently added Community Hub searches. A search for Dyad shows an update called "ValveTestApp223450." A tweet on the official Twitter account for Dyad from earlier today seems to confirm an upcoming release, reading "So I wanna do a proper announcement about Dyad coming to Steam, but that kinda got ruined. March." A tweet published about an hour later revealed that the developer has created and is uploading a launch trailer.
Searches in the database also reveal listings for Halo: Combat Evolved, Halo 2, a Steam Community Hub for Halo 3 that was later removed, an app for Duke Nukem 3D: Atomic Edition, Fez, whose developer announced late last year that the game would be expanding to other platforms, and many more.
As Stumpokapow writes, the listings could mean that these games are coming to Valve's digital distribution service. It might also mean that Steam Community, a recently revamped service that contains a hub for game-related content like discussions, screenshots and guides, will support non-Steam games, including console titles. It seems unlikely that the Halo games would come to Steam, given that they're published by Microsoft, which just launched its Xbox Games on Windows 8 service.
When contacted by Polygon, Dyad creator Shawn McGrath shared the below YouTube video containing the game's official announcement for Steam. The game will be available through Valve's service in March.
We've reached out to Valve and will update this story as more information becomes available.