First Draft of the Revolution is a browser-based, interactive, epistolary story, where the process of letter writing is used to explore aspects of character and plot that might otherwise remain hidden. Plus, lashings of classism and magical references.
Dead Cyborg has the heart of a text adventure within the body of a 3d engine (youtube trailer). Caveats: donationware - future episodes dependent on donations. burster plug-in required for browser play
Metaplace Raph Koster's customisable, isometric, browser-based 3d environment has now entered open beta. caveats: Registration required, some Beta flakiness (previously)