Here is a paper by Dunn on semantics for relation algebras... one of these days I'm going to understand what the heck this "gaggle theory" stuff is about. Galmiche and Larchey-Wendling's Quantales as completions of ordered monoids: Revised semantics for Intuitionistic Linear Logic also looks to be a fairly readable discussion of (properly nondistributive) algebraic semantics for linear logic.