Advice – GPS Tracking for Web App

We're working on a fleet management solution for a client, and I'm looking for an app for iOS and Android that captures GPS locations for several devices and submits those locations to a database we can integrate with for display on our own web app. Everything I'm seeing is focused on their own proprietary software and mapping (I understand why), but I can't imagine this is a very unique use case. Any advice would be greatly appreciated.