SkyCharts v1.4.4 and greater is using RouteMe to display the maps.
Backend tools on linux use GDAL to create the maps.
Some icons are from Wikimedia Commons, like the P51 airplane silhouette, and states.
Satellite Tiles Courtesy of MapQuest
Portions Courtesy NASA/JPL-Caltech and U.S. Depart. of Agriculture, Farm Service Agency.
ONC charts from the University of Texas:
“Used by permission of the University of Texas Libraries, The University of Texas at Austin.”
SkyCharts XC and LightBox Extra for iOS/Android/FireOS is built using:
Big thanks to BinaryCart for their demo of the tools.
SkyCharts XC uses Leaflet for the maps.