You are downloading the Preview for Developers XAP file v184.108.40.206 for Windows Phone. Preview for Developers is a free Productivity App: Now registered Windows Phone developers can receive pre-release OS updates on their dev phone, directly from Microsoft! You can use this app to opt-in your. You can now download the offline XAP package file to install & try it.
Download Locations for Preview for Developers 220.127.116.11 XAP file
To try to install it manually from an SD card, you should choose one of the server location above to get the offline Preview for Developers XAP file, move the file to your phone's SD card and then tap 'Install local apps' in the phone's App list.