The grid reminds me of Triple Triad from FFVIII (Also available online by fans and online bundled with FFXI), and Eye of Judgment for PS3. Alteil's gameplay feels unique to me though. I've played Magic/Duel Monsters/Pokemon/Yugioh/Warcraft TCG and a few others but I think Alteil strategically isn't too similar to them. I would agree that Duel Monsters is probably the most similar to Alteil, with the shields concept being pretty much the same as the Soul Cards except it doesn't go by order. I think the reason Alteil feels unique is because it gives you access to your entire deck, and the only other card game I've played that does that is Spectromancer.