None. Not saying you shouldn't use any, but I always keep my watch stock, and I think it's good practice especially right after release to not mess with too many 3rd party apps.
The whole point of these devices is that you can customise them to your exact needs using CIQ. I have gone as far as learning how to program for CIQ so I can make my own apps to fulfil very specific needs. As many of them are not published a list is a bit pointless.
Third party apps and datafields might at time crash (the 945 has a faster processor than the 935 and that caused me a few issues with my own datafields) but that generally doesn't crash the whole watch and certainly doesn't do the watch any damage.
While you might have to be a bit careful with some CIQ apps, if you stick with apps with good ratings/reviews you should be fine. Starting a while back, Garmin itself has been been using CIQ to add functionality, with the music apps and RunPower data fields being the most visible. On the MARQ devices, some of the specialized functionality of the different models is also CIQ, with the "Driver" app for the MARQ Driver as an example.
I did find one app that caused the watch to crash (Battery Widget which I ran on my 935 without issue) , removing it and restarting the watch solved the issues it was causing. Big fan of Garmin opening up the ecosystem which breeds innovation - all good for users of the products. As this is brand new hardware I would expect to find some more issues as apps are added to it, but the developers are usually pretty quick to release updates when they get notified of bugs.
Garmin Explore looks like it will be fantastic for finding routes to run/explore as I travel. But it so far won't pair with my 945. Similar problem I had with apps on my previous three Garmin watches that use apps. Miss my old 305, last Garmin that did everything without complaint. Exploring Suunto, maybe time to end my long loyalty to Garmin, I can still return my 945.
