There are two ways to earn free bitcoin apart for mining (as mining rewards are very low, so this is not a viable option anymore until you want to invest in good hardware.)
Use Referral Program : A lot of companies are now offering good referral programs to earn free bitcoins. You can try CoinSwitch New Referral Program where you can earn $5 for every successful referral.
You can participate in airdrops to start earning fee token. Although a lot of them will not have any value, but some of them may get to a significant rise in value if the project is good. Eg. ONT which gave 1000 ONT as Airdrop and now its worth over $1800.