Garmin Connect is described as 'Community-based website for runners, cyclists and outdoor enthusiasts who track their activities with Garmin devices. Garmin Connect makes it easy to upload, store, analyze, map and share activities online' and is a Run Tracker in the sport & health category. There are more than 50 alternatives to Garmin Connect for a variety of platforms, including Android, iPhone, Web-based, Apple Watch and iPad apps. The best Garmin Connect alternative is OpenTracks, which is both free and Open Source. Other great apps like Garmin Connect are Strava, ASICS Runkeeper, MyFitnessPal and Runbuds.
It doesn't support the use of external GPS trackers. It ONLY supports phone GPS.