Repeater-START, the only open-source offline repeaters mapping app, is available on Github, and Sourceforge.
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GMRS, like ham radio is a licensed FCC system with frequencies and repeaters. To add a region, copy a url below:

Oregon GMRS:

Latest listing is on their official website http://oregongmrs.org/

Copy this to the add repeaters area in the settings area:

To add your own list please contact contact @ hearham.live.