As the most actively developing App on the SAFE Network right now, SAFEx could be the first major breakthrough realized on the SAFE Network. Not just an exchange, SAFEx is an attempt at a core, underlying protocol for p2p trading on the SAFE Network, and there is no limit to what it could do.
The brainchild of Infinity Algorithms CEO Daniel Dabek, SAFEx has been in development for the past 3+ years, and is the result of Daniel's history in the high-speed trading and finance sectors. He aims to remove much of the human struggle & error from the equation of high-speed internet finance. Daniel is 24 years old and works with the SF SAFE Pod, among his other ventures.
In addition to the 2D SAFE App, which people may use to trade anything from dogs to doges (and possibly even gaming currencies, as pointed out by blindsite2k,) SAFEx now has a completely immersive port into a 3D MMORPG-like trading floor (see it here!), completely modeled in Unity. This allows anyone in the world to immerse themselves--either with a screen or using VR--with their trading, and walk up to actual avatars to fill their orders.
It was expected that the network would launch at the end of last year, (and this app soon after,) however an amazing new coding language came out called "Rust" that turned out to be perfect for the SAFE Network to be created with. So, the team decided to restart the whole network from scratch in Rust. This means we will have to wait a few more months to see the network or this app. Follow it on Github!