MakePlayingCards is described as 'Create your own custom card designs for card games, tabletop games and more'. There are four alternatives to MakePlayingCards, not only websites but also apps for Windows and Steam. The best alternative is Anime Yu-Gi-Oh! Card Maker. It's not free, so if you're looking for a free alternative, you could try ADL Interactive or nanDECK.
nanDECK is a software for Windows (any version) written as an aid for game inventors, with the aim of speeding up the process of designing and printing deck of cards (useful during prototyping and playtesting).
Card Creator is a Windows desktop tool for creating card designs for card, tabletop and other types gaming. Create any kind of cards without coding or drawing, using any card formats you can imagine using the Card Blueprint tools.