Re: Dungeons and Princess (DMM)
The magic stone (purple colored stone) can be used to fill your stamina, or play random draw for a chance to earn rare cards (I think all R level cards are gained this way). You can use FP for it, but I think magic stone give a slight better chance to score rare card and you can get their evolved form (Which is not the ideal way if you want max out status, since if you fuse both card with max level they gets slightly better status).
Other items are used in daily or card quest (most card which can evolve give you quest). The reward can range from money, other items, exp books, and I think unlock their second scene eventually (Haven't confirmed this).
exp books in addition of giving a bit more exp, also gives 覚醒exp to cards. Basically, some evolved form of the card has a 覚醒exp (roughly translate into 'awaken exp') bar under its skill tab. Once you fill that bar up to max you unlock a skill for the card (I think it's the second passive skill of the card, has to do more test to confirm this for all cards).
Compare to LoW I would say D&P is a bit weak on the gameplay side (you don't have equipment or an avatar to wear them, and the battle AI for your cards is the walking defination of dip shit), but personally I think the H scene you unlock in this game is better than LoW. Just my prefence though since I didn't like LoW's more chibi style. But gameplay wise my favourite game on that website is Goddess of Defense, a rotation defence game with RPG element.