Bike share systems have these kinds of apps because the racks or kiosks have some smarts in them and can communicate their status. Normal racks don't would depend on people sending updates which couldn't be relied upon.

Someone could create an app that would let folks add the location of racks that they know about, how many spaces they have and how full they typically are. A comment area would be nice so that others could provide further details saying perhaps that the rack had been moved or that it's almost always full unless you get there early. An app like that might exist but I don't know of one.

As an alternative you could use something like Google Street View to get a feel for where it is you're going and if you're likely to find a reasonable place to lock up your bike.