First there was A Uniform System of Citation (1926), which everyone called The Bluebook and eventually began calling itself by that name. The Bluebook was spawned by Harvard (or Yale, depending upon whom one believes). It mutated over the years into quite a hideous thing, but it nonetheless became The Standard that everyone used.
Along came The Maroonbook (1989), which seemed promising at first but quickly degenerated into a mess of its own, and in any case didn't really matter because the only person who even noticed it was Judge Posner, who never liked The Bluebook anyway.
The legal writing directors jumped into the fray with the ALWD Citation Manual (2000). It was just as long as The Bluebook and even more expensive. Like The Maroonbook, it was inconsistent with The Bluebook, and was generally ignored and occasionally scoffed at by lawyers, courts, and law review editors. ALWD threw in the towel for its Fifth Edition (now called the ALWD Guide to Legal Citation), adopting The Bluebook's citation system and merely attempting to describe it more coherently (though still at a higher price).
Finally, in 2016 came Carl Malamud (Public.Resource.Org) and Chris Sprigman (NYU Law) to save the day, with Baby Blue's Manual of Legal Citation, an "open implementation" of The Bluebook's citation system placed into the public domain (i.e., free). Naturally, the Harvard Law Review Association is trying to block Baby Blue. But it shouldn't be hard to choose a side in this battle.