BlackCoin, abbreviated as BLK, is a digital currency that uses a proof of stake system to facilitate secure and anonymous transactions between peers. It is open-source and can be audited by anyone making it completely transparent.
Ever since its development and launch by Rat4 back in 2014, the distribution and user community of BlackCoin has grown by leaps and bounds and has established itself as a future leading contender in the cryptocurrency space.
The BlackCoin system is not only safe, but also one of the fastest in transactions in comparison to other digital currency systems.
If you want to know more then check out the full Blackcoin Wikipedia article.
A very nice, short and to the point Blackcoin guide. How it works and came to be.