Adventurer Conqueror King System, or ACKS for short, is inspired by the basic and expert version of the original D&D, with a touch of modern and also some inspiration from AD&D 2e edition.
First, the name comes from the various stages in the life of a character. They start out as adventurers, then they conquer a territory and then rule it. The name reflects well the rules as the system goes into much details in areas where other rules sets leave the GM on his own. In ACKS there are detailed rules on construction of a stronghold, management of a territory, trade, etc.
The rules take much from B/E D&D: the highest level is 14, races are classes, the cleric has no spell at first level, and the thief has a d4 for HD, etc. ACKS adds multiple choices for many race/class, instead of just a dwarf, you have the choice of playing either a dwarven vaultguard or a dwarven craftpriest, instead of an elf, you can play either an elven spellsword or an elven nightblade. Race/class are limited in the highest level they can reach. Only human characters can reach the 14th level.
The game adds proficiencies, more like those in the 2e edition of AD&D than the feats of later editions. These add some customization to character classes and also define a number of rules mecanics and structure to the rules.
ACKS keeps the concept of THAC0 but uses an ascending armor class. It also uses a unified characteristics modifier, but keeps the class specific saving throw tables.
I came to ACKS from years of playing AD&D and there is a lot that I like in ACKS. I initially looked at it because I got a copy of the ACKS-compatible megadungeon Dwimmermount, but I really like the rules and look forward to trying them out later this year.
Here are a few things I made for ACKS.