ACKS_SRD VS microluxe20

The ACKS SRD is though!

I can't help but notice you have an interest in wargaming. Adventurer Conqueror King is based off of B/X and is pretty simple in the low levels, but then gradually expands into domain play and wargaming with Domains at War in the mid-high levels. There's an SRD for the non-DaW stuff if you'd like to get an idea of the complexity of the main RPG part of the game without dropping any spend.

For those who might want a look at the domain management rules without purchasing the product, there is an ACKS SRD available on github. The relevant section is in chapter 7, then search in the page for "Strongholds and Domains".

ACKS has Domains at War for mass combat at various scales, and an emphasis on domain play generally.

ACKS has proficiencies which are feat-like. Many of the classes in the non-core books also have multiple "paths" per class (ex the barbarian comes in jungle flavor, steppe horseman flavor, and norse flavor with slightly different abilities).

ACKS SRD on GitHub: https://github.com/jhhoffmann/ACKS_SRD/blob/master/Chapter00.md

ACKS was the first OSR game that I ran successfully, coming from a 3e background. It's mostly B/X plus feats (proficiencies), semi-spontaneous casting, a couple of small but high-impact buffs to the fighter, and backports of some of the more modern classes. Pretty good DMing and setting-building advice in the back of the book. The text isn't as stripped down as OSE, which may make it a little more accessible for first learning. Free SRD here.

Adventurer Conqueror King System; here's the SRD.

ACKS might be worth considering. All throws are on d20 roll-high and it's semi-race-as-class (multiple classes per race, but unique class-race combinations). The attack throw system is a little wonky on paper but plays very well in practice.