The Wifi was turned off on the Crystalsky... I dont think that you can install a custom Go4 app onto the Crystalsky... Unless someone has proved this workable, I'd be too concerned that in doing so I'd loose the existing version on the device.
Apps that work.... Download Yalp of the net first and log in with your Pay Store details. Download the below apps through Yalp straight to your CS. Just type wanted app name into search bar in Yalp. Not pretty like play store but works. Yalp will download apps that you have purchased in the Pay Store, but the CS can't confirm purchase so they won't work.
Mavic Pilots app - this forum
Lightroom - photo editor
Photoshop - photo editor
Google Chrome - internet (no sign in/sync)
Firefox - internet
(sync works fine)
VLC - media player
Compass - obvious!
Kodi - media player
Facebook - unfortunately (incase I actually want to share instantaneously... not that I ever use Facebook).
Google translate - in case youre flying elsewhere
Done Code - show your rights to the pesky doubters passing by... and know your rights
WOL - Wake On LAN (turn on remote NAS drives attached to same WiFi
Kittyhawk - to let you know where you can fly etc
LightWaveRF - switch the pre setup charger on by remote from any location.
Netflix - video player
Yalp Store - update apps on the the CS and also download apps from the Google store
Gboard - Google Keyboard (swipe your heart out)
Instagram - photo share (doesn't format and edit options are off screen... edit in lightroom instead, then share to Instagram)