In a free way, it is unlikely that you will get tokens, even bounty and airdrop require effort and time, so if you want to get tokens you should either invest or participate in bounty.
These two things you will do because you need time to produce something that you can get seems to follow the bounty.
I think the only way to get a free token is to joined airdrop, airdrop is really the number one ways to earn or get free token but we can really earn a verry few amount on it, bounty is not considered as free because we need to work to have a token as a salary of our effort, same with investing, investing an ICO is not really free you have to pay for it and even if they have 20 to 30% bunos amount of token that is not considered as free because you cannot have it if you are not an investor.