I imagine one of the first questions someone might have about Hand of Fate: Steam and Sorcery is, "Why use playing cards instead of dice?" There are actually multiple reasons for the change, and I'll try to cover the main ones here. Note that if you remain unconvinced and want to stick with dice, there will be a section describing several ways to do that, either using d12-d12 or the standard 4dF / d6-d6.
1) Setting: In the 19th Century, gentlemen and ladies played cards, and only the lower classes would play dice games. Whether you are playing in the American old west, a private club in Europe, or a casino in Monaco, you generally think of playing cards. Using cards in the RPG thus helps evoke the feeling of the setting.
2) Availability: Fate games typically use Fudge dice, which can be hard to find until the Fate Dice are released. Most people have a deck of cards though, and if they don't, they are very easily found.
3) Style: There are some great-looking decks of cards being made today, and many of them have fantasy or steampunk themes. Several years ago the U.S Playing Card Company, makers of the Bicycle brand and the leading manufacturer of playing cards in the US, began allowing ordinary folks to submit a design and pay to have their own custom decks made. This started a boom in the playing card market as everyone from magicians to design studios began creating decks. There are now many dozens of unique and beautiful decks of cards and more being created every day. This means each player can choose a deck that suits their character, and the GM might choose a different deck each week that suits the adventure... a magical looking deck if they are facing a cabal of evil mages, a deck with skulls if they are fighting undead, a steampunk-styled deck for a mystery aboard an airship, or an Arabic-themed deck if they are lost in the Sahara.
4) Additional Information: The card suits, colors, face cards vs number cards, and the Jokers all give opportunities by providing additional information that a dice roll doesn't have, and I've incorporated all of those things into the game. For instance, if your card matches the color of the task you are attempting (black cards for physical tasks, red cards for mental/social tasks), then the card's value is positive. If it's the wrong color, it's negative. This means every card in the deck is potentially positive or negative, it just depends upon when it comes up.
5) Strategy: By replacing your Fate Points with a hand of cards, and being able to substitute a Fate card for a randomly drawn card, there is a new element of strategy to spending your Fate points. If you are holding a good red card in your hand, for instance, you might attempt a mental or social test where you might ordinarily be weak because you can then play that card by invoking an aspect. And whenever you draw or play a Joker, you have a chance to trade in some or all of the Fate cards in your hand for an equal number of new random cards... do you want to trade that card that you haven't found an opportunity to use yet in hopes of getting a card you like better, or do you hang on to it? Questions like these are only possible when you have a hand of cards rather than a fistful of dice.
6) Greater variety of results: I prefer games with a bit more granularity, where a +1 or +2 isn't a massive bonus, and the likely results of most tests is greater than 3-5 numbers (-2 to +2 is common, with -1, 0, or +1 being the majority of results. A deck of cards goes from 1 (Ace) to13 (king). In Hand of Fate, you draw 2 cards and use the lower one, and the result is 0 is both cards are the same value. This is the same method as d6-d6, but with twice the range of possible results. This means I can have some + or - 1, 2, or 3 modifiers on some things without that being an overwhelming factor.
7) Uniqueness: Relatively few games use playing cards as the primary or sole means of determining success and failure at tasks. I wanted to create something that was different and stood out from the rest, and using cards instead of dice helps make the game unique.
So, those are my main reasons for using playing cards instead of dice. I'll leave you with a look at some various playing card decks to give you an idea of the range of possibilities in decks.