While Chronokings (which is still in development) is intended as a full-featured serverless MMORPG and crypto-currency, Huntercoin is designed as a kind of crypto-currency with manual mining.
It is too simplistic as a game, but serves its purpose as a crypto-coin. Computational mining is still required to keep the game running, but miners only receive ~10% of the block reward. The rest is to be collected by players. To keep miners interested we allow merged-mining with Bitcoin, Namecoin and Litecoin (and possibly other currencies that support SHA-256 or Scrypt merged-mining). Miners will also receive a small percentage of coins banked and when a player with coins is killed.
The idea of a manually mined coin is not new, for example there was proposed a CAPTCHA-based coin. However, this concept was flawed, since CAPTCHA and other machine-to-human challenges depend on a hidden state that cannot be implemented in a decentralized way. The block-chain must contain deterministic information to generate the CAPTCHA, thus the solution can be trivially obtained from it.
Instead of the machine-to-human challenge we present a human-vs-human challenge, where players compete to get coins from the game. To our best knowledge this is the first manually-mined coin.
Difficulty adjustment of the block-chain is based on block mining to provide approximately constant move timing for the game and constant generation rate of coins (both miner reward and game reward). We can also notice that there exist a virtual in-game difficulty: as price of coins rises, more players will participate in the game and it will become harder to play. Moreover the players will become more aggressive to each other, but also may form coalitions to hunt for coins more efficiently and split the loot.