Byteball is a cryptocurrency platform, which uses directed acyclic graph (DAG) instead of blockchain. In a blockchain all the transactions are joined into blocks, and a block can be mined (a special signature should be found by one of the nodes). In a DAG most of the transactions are asynchronous: a transaction occurs when both seller and buyer are ready to sign two legs of the exchange. Byteball is an open source project, initially started in September 2016 by a team of Russian developers, but now is international. Byteball operates with coin called byte.
Main differences from classical blockchains are atomic exchange (through DAG), possibility of multi-signature and textcoins. Despite atomic exchange, vendors can issue regulated assets, which require co-signature of the issuer, so the sale complies with anti money laundering regulations. Textcoins is an option to send cryptocurrency via email or chat. Multi signature means that to spend funds two or more signatures are required, this is used for shared control funds.
Another feature of Byteball is that 99% of its currency (byte) is being distributed for free through cashback deals and referrals.