The current version of the Dai stablecoin is collateralized solely by ETH, and recently eclipsed 100 million in total supply. Multi-Collateral Dai (MCD) will be collateralized by a basket of ETH and ERC-20 tokens, as decided by MKR token vote. The community is currently evaluating BAT, ZRX, GNT, DGX, REP, and OMG for inclusion in the initial version of MCD. Existing single-collateral Dai will be continue to be supported as a seperate token for the near terms, with users encouraged to migrate assets. Another key change is the ability for CDP holders to pay the stability fee (effectively an interest rate) in DAI, previously in MKR. Dai is a key building block for much of the Ethereum DeFi space of applications, and is frequently used in lending protocols such as Compound and various DEXs.