I'm building an exchange service where I have all users deposit ETH and ECR20 tokens to a single Ethereum address (In order to avoid complications of having to consolidate funds & paying extra gas fees to transfer/forward each deposit to a main account when using 1 deposit address per user). In order to efficiently track user deposits and credit the right user for his deposit each user will be forced to first "link" their external wallet to their wallet account on our platform. Once they link their wallet to their account I can credit any deposits made from the external wallet address to the owner of the account. I believe Cryptokitties uses a similar concept.
However, I don't want to force all users to have a MetaMask account in order to use our service so I'm interested in knowing what other wallets/services support Login With MetaMask concept? I'm looking for a broad spectrum of services that support this concept so that ours users would be a able to deposit ETH + ECR20 tokens regardless of where they choose to hold/store their coins..