The Justified Ancients rules are written by Pete Blockley. Find out about them on his website.
They are worth a look - take a look at my review if you want to know more. I have used them to game chariot battles in antiquity, classical Hellenistic battles and mediaeval battles, and the rules have worked well in each case, producing realistic results in reasonable playing time.
I am a constant tinkerer with wargames rules. Here are my latest house rules (PDF). These are still under development, and not all of them have been tested.
I have produced a quick eference sheet (PDF) to help streamline play. I also have a modified copy including my house rules.
Here are my current thoughts on JA troop classifications for tthe armies I've used. This is an important element of JA, as the rules themselves offer little advice on how to classify your armies. Experience has shown that troop classification needs to be done with care if you are trying to model historical battles (or, in fact, just trying to have a realistic game). Changing the classification of a few troops can change the whole flavour of a battle; for example, I couldn't decide for a long time whether Alexander's Companion cavalry should be graded as Loose Order or Close Order. It really makes a big difference in how they play on the battlefield!
Here are some battle reports: