I'm just wondering if it is safe those who are giving free coins asking for private keys, and saying that it is safe they don't store it?
The usual sample is asking you your ETH balance, then a certain coins balance, and it will generate how much coins you will get based on your ETH and a specified coin balances. Then they will ask for your Private keys.
I just passed by all this coz I don't want to compromise my wallet for few tokens.
Don't ever give out your private keys, i don't really know if you're talking about these scam emails / Slack / telegram messages that have been going around
or just general. You will need to use your private key(s) though to claim forks and even with legit projects you should always empty your wallet before you enter your private key into
the (official) wallet software. For example Bitcore (btx) a BTC fork explicitly tells it's users to empty their wallets before putting in the private key as a simple security measure