I don't use too many third party complications on the watch, but there are 4 that I find useful
1.Stocard is great for storing my store loyalty cards
2. Thermo Watch for controlling my nest thermostat
3. WeatherMate Pro for looking at the weather
4. Sundial to check for dawn & dusk to help plan outdoor runs during the winter months
Plus a few more that I see occasionally
1. Weber iGrill for grilling
2. Speedcheck - useful for checking my internet speed while out. I almost never need to do this & have only used the app a handful of times, but it did come in handy when I did
3. Workoutdoors - I use the built in Apple workout app for exercising but I do like to use workoutdoors when I travel, as I can preload routes for areas I'm not familiar with.