The $4 Mattebox app looks simple, but it's actually a photo app built for photographers who are used to shooting with fancy DSLRs. The user interface is modeled after a famous camera made in the 1990s, the Konika Hexar, and it uses that camera's viewfinder as inspiration. Mattebox displays information pro photographers expect to see at a glance: ISO, white balance, shutter speed and focal distance. Only white balance can be manually controlled due to the iPhone hardware, but all that information is on display for photographers to keep in mind while shooting.
One of the app's coolest features is a dual-stage shutter button, or slider. By holding down the button, you can lock exposure and focus, then adjust your framing before sliding the button down and snapping a shot. Mattebox also offers some basic editing tools for cropping, color, exposure, gamma and saturation tweaking, but the unique viewfinder is its primary draw.
If you want filters, check out the next app: Camerabag.