For years, I've tried numerous slim wallets that carry what I need without the bulk. After building this wallet for myself and some close friends and after testing it for a year, I hope others will appreciate it and find it useful.
 
I find that each slot fits two cards comfortably, which brings the total capacity to at least 8 cards and probably a few more if you don't mind stacking them 3-deep.
 
The center of the wallet opens up to fit cash, receipts or whatever weird stuff you like packing around.