Bitcoin mining pools
First blocks in the bitcoin blockchain was mined on PC by solo miners. When bitcon get some popularity in the crypto-geeks community, new mining method was born - bitcoin mining pool.
Pooled mining allows many miners to work together and therefore reduce variance in their Bitcoin reward over time. This is achieved by fairly distributing the reward from any blocks found by the server according to how much work you as an individual miner have contributed. The block reward and transaction fees are paid to the mining pool. The mining pool distribute rewards between individual miners. Different bitcoin mining pools use different reward distribution systems.
BTCMine in the past was one of the first bitcoin mining pool back to 2011. Later that pool out of business because most of miners migrate to the new pools with Stratum mining protocol support and domain was sold to new owner.
Today's several giant mining pools controls over 95% of bitcoin network mining power. The biggest mining pools now operated by Chinese owners. This situation happened because almost all modern mining hardware "Made in China".