Tauchain is a project made up of a meta language (TML) a collaborative development, and a consensus mechanism. Tau Meta Language (TML) is the core element allowing you to communicate to machines so think of it as the ultimate compiler although maybe compiler isn't the most accurate term. The collaborative model checking element is part of what allows for the collaborative development mechanism to be enabled by program synthesis. The consensus mechanisms is up for debate but Ohad and some others favor proof of work while I favor delegated proof of stake (similar to Graphene). I see no good reason for the waste and inefficiency of proof of work when the security in practice is pretty much the same as what you get here on Steem with delegated proof of stake. Of course this will be the first real debate and the Tau discussion component is one of the most important because it will allow us to arrive at a solution which satisfies most of our collective requirements.