Duelingnetwork.com

My friend got me to start playing Yu-Gi-Oh, as if it were still popular, through this site.

It's a Yu-Gi-Oh tabletop simulator/deck builder. Not sure if it's legally hosted, but it's got no ads or downloads or anything so it's safe at the very least. Not to mention they're the only ones liable for the site itself.

Entirely free, all the cards available, standard and traditional formats, rated and unrated games available. Got a rating system and leaderboards... my only complaint is that everything is manual so you need to make sure nobody is breaking the rules, and report them if they do. It's just like being face to face with the cards, except not.

Check it out if you like card games and free things, don't check it out otherwise. Just thought I'd throw it out there for you.

Can't beat the price of "free!"
I may have to check this out... despite having never had an interest in Yugioh.

That's the spirit! Everything is worth a try for free

If it's a free card game you're interested in there's a similar online thing to MtG called 'Elements' it's quite good, just throwing that up here. =)