None other than ETH. Why?
 1)The mother of all erc20 based tokens
 2)Vitalik Buterin as the founder and developer.

I've downloaded the app just now after a member of the group I belong to has posted about it. Though it seems like a bit of "too good to be true" app, further research answered my question as to why claiming of ETH is "free"; it's all about the Ads (lol). After clicking the claim button you'll have to wait for 2 minutes and eventually a pop-up Ad will appear on your screen (regardless of what you're doing). It's in an incremental value of .0001/claim. Plus you'll get an additional reward for every referrals. More like a networking strategy though. Anyway, so far so good, it's worth a try. Just be careful as there's a rumor that some users (esp. those with android os) ETH are being stolen through screen recording scheme. So this app is a no exemption.