Kevin Crawford simply writes good shit. If you want an OSR game that isn't simply fantasy, that is built from the ground up for sandbox play, pick up a Sine Nomine ruleset.
Kevin is probably best known for the sci-fi RPG Stars Without Number: Original Core Edition (on sale for 11.99). There are also Silent Legions (Mythos on sale for 11.99), Scarlet Heroes (on sale for 8.99 for one on one swords & sorcery play), Godbound: A Game of Divine Heroes (also on sale for 11.99), and other titles.
Seriously, it's hard to go wrong with Sine Nomine :)
You can catch the daily Tavern Chat podcast on YouTube - Tenkar