Because I hold Bitcoin, I was given about the same amount in Bitcoin Cash at one point.
I was also given some Stellar (XLM) for free.
Does anyone know if this is regulated in any way regarding taxation? My Bitcoin emerged out of fiat. But this came out of nothing!
Tax regulations cover all cryptocurrencies.It doesn't matter if its BTC,ETH,Stellar or Bitcoin cash.
The rules are the same for all coins.Coins,that were created after a hard/soft fork are no different than mined or bought coins(at least in the eyes of the tax agencies,that might consider forked coins to be a capital gain),so they are taxable as well.
In which country do you live OP?
You say that you were given Stellar for free.Maybe this can be considered as a donation and deducted from your taxes.I'm not an expert.Perhaps you should talk to a professional accountant.