Using Google Play Services Leaderboards

Heroic Labs Documentation

The Give and Go: Leaderboards

How to build a real-time leaderboard that's serverless, fault-tolerant, and scalable. - GoSquared Blog

Leaderboards Reference - Core Documentation

Leaderboards and tournaments

Leaderboards in Gameful Design: Their effects, types, and guidelines for their correct use, by Gustavo Tondello, Gameful Bits

ggLeap Leaderboards

Leaderboards: Example of Implementation - GOG Developer Docs

Start a competition with IXL Leaderboards

How to Design Leaderboards: Boosting Motivation & Engagement