Tracker.GG is described as 'tracks over 100 million players across popular games like Fortnite, Apex Legends, Destiny, Rocket League and more. Find detailed stats on players, check out the leaderboards and more'. There are four alternatives to Tracker.GG, not only websites but also apps for iPhone, Android, Android Tablet and iPad. The best alternative is OpenDota, which is both free and Open Source. Other great sites and apps similar to Tracker.GG are Dotabuff (Free), StatsNite (Free) and Plink.gg (Free).
OpenDota is a volunteer-developed, open source platform providing Dota 2 data. It provides a web interface for casual users to browse through the collected data, as well as an API to allow developers to build their own applications with it.