If you are a person that wants to develop with GeoPosty on your localhost or if you are developing locally to your webserver (on the company network or whatever), then you will be happy to know that the newest version supports just that.
To get started:
1) Download and install the newest version of GeoPosty here: http://wordpress.org/extend/plugins/geoposty/ OR install the plugin from the wordpress repository through the WordPress admin by clicking “add new” in your admin panel.
2) Obtain localhost development key here: http://www.geoposty.com/request-your-test-api-key/
*Please note: you will need to update your API key before going live to the API key for your domain.