This report explains different types of Blockchains as well as different consensus algorithms.
Blockchain is a distributed ledger that consists of a chain of blocks. The study focuses on the Ethereum platform, as it seems to be a promising platform for the execution of so called smart contracts. Smart contracts are autonomous applications which are executed in the Blockchain network. This provides applications with no downtime and high censorship resistance. Based on the Blockchain technology and on smart contracts a messenger was developed.