hackattic - No nonsense, real world programming challenges
SaaS Starter Kit - A starter template with Docker, Kubernetes, CI/CD and more
Codewars - Achieve code mastery through challenge.
Nextacular - An open-source starter kit that will help you build full-stack multi-tenant SaaS platforms efficiently and help you focus on developing your core SaaS features.
Real Dev - Real-life coding skill challenge
UseGravity.App - Build a Node.js & React app at warp speed with a SaaS boilerplate