Recently, EthBattle team https://ethbattle.io has introduced the new concept for the crypto gaming industry, allowing people with only Metamask installed, to play EthBattle, making 'free' bets and been rewarded with real Ether back.
The idea, in a nutshell, is that every free bet is a sort of a microloan, and it's taken back in case of the win.
This basically means, (at least for now) that everyone is able to play EthBattle with Metamask only and no ETH on the account, taking zero risks but been rewarded in ETH in case of the win.
Enjoy!
https://ethbattle.io