OSR as a community and a movement is as heterogeneous as what the 'R' in OSR actually stands for. I'm fond of 'Revival', though 'Renaissance' is often used and is perhaps even more accurate. 'Rules' or 'Retro-clones' can apply but seem specific to games that celebrate old school mechanics or design, for example, treating demi-humans (such as elves) as classes unto themselves, foregoing the notion of a race/class combo. I prefer broader terminology so as to include additional aspects of old school games, such as play style, aesthetic, and table values.
Unique to OSR, I experience a flurry of wonder and anticipation that parallels the first time I saw Larry Elmore's red dragon on the Red Box of old. I'm the kind of gamer that can take pleasure in the mere reading of an RPG system and consequently own many that I've never played, if primarily because my friends are unsympathetic to my pleas and want to stick to systems they know!
Larry Elmore's cover art for the Dungeons and Dragons Basic Set (1983 Frank Mentzer revision), known as the Red Box.
The marriage of players to systems was something my younger peers and self never considered as we moved seamlessly between games, with little to no prep, on a whim. This was largely a dividend of our play style at the time. For many, the rulings not rules and rule of cool play style is OSR essential, and discovering how rules affect the experience of play is a journey for every game designer.
Play style, rules and mechanics, aesthetic, and table values all contribute to the sensibility of an OSR game. It is the cultivation of an experience defined by mystique and the unleashing of imagination. Through the changing demands of the consumer and the maturity of the industry, some essential part of the classic experience was misplaced. This is what we seek.
But isn't that just nostalgia? you ask. Why not just play those old games?
The OSR movement has spawned a lot of games with a range of play experience, some using modern rules. No matter how heavily influenced we are by classic games, it's important to acknowledge that the old ways weren't flawless and that modern gaming isn't without its merits. There is plenty of room in the OSR movement for a modern approach to old school values.
Why am I rambling on about OSR? Is Heroes of Happenstance OSR? A critical design pillar of HoH is accessibility. It is meant to be light, fun, and approachable. That it can be played without a GM works toward that purpose but may affect its "old school" credibility. For now, it is described as having a "classic aesthetic". When development reaches maturity and we begin play testing, perhaps we'll revisit this question. For now, it's enough to say that the work and creativity of the OSR community is inspiring.