First, let's define speed trap a little narrowly as locations that use false or misleading or missing signs to trap motorists who believe they are driving within the limits--that's different from locations set up to stop people intentionally violating limits. I don't know about apps for that, but AAA has (or used to) a list on their website.
The app you cite does not make that distinction; it says that "Users submit speed traps, enforcement cameras, and road hazards, that then alert all Trapster users in the area. A high-tech version of flashing your headlights to alert drivers of potential road hazards." It also uses misleading statistics to promote itself (see chart below). It reports 20 million reports as 20 million users, without indicating how many distinct users (as in 10 people making 20 reports each=200 users) and gives an absolutely absurd figure of nearly 7,000,000 traps--that must surely include multiple reports of the same locations.
As far as traffic and road conditions, I mostly use Google Maps/Navigation, which does a pretty good job of keeping up with traffic conditions.