I use:
TPE
NDFilterCalc
PhotoPills - big suite of useful tools, check it out
Sun Surveyor
TiltLens - calculates tilt angles for Scheimpflug
#UKSnow - map of snow falling in the UK updated by twitter users
WeatherPro - hour by hour weather forecasts, I've found it to be near enough spot on accurate
MeteoEarth - integrates with WeatherPro with broadcast standard weather maps, precipitations mapping, satellite etc
Live Lightning - tracks lightning strikes
UK Tides
Deluxe Moon - calendars of moon phases, apogees, moonrise and set etc, very powerful