It's an EHR... with no actual EHR logic in it. It's just a front-end to a proprietary service, zapEHR, that does all the actual heavy work of being an application.
If you think the heavy work is solely in the back-end, I'd encourage you to go ahead and try to build and release a front-end. We would happily use yours if it were good. We built the Ottehr front-end after building "the proprietary service" and realizing just how difficult it was to actually release an EHR without a front-end reference. You are also welcome to point Ottehr at some other back-end service if you want. Our goal is to encourage a new generation of EHRs that better support interoperability.
The acronym EHR is not explained in the readme or on the website that it links to, but it's used a million times. Dictionary (merriam webster) doesn't know it either. Great EHR software I'm sure, but what's EHR?