What are some alternatives?
When comparing Code4Startup and Frontloops, you can also consider the following products
Quick Code - Curated list of free online programming courses
hackattic - No nonsense, real world programming challenges
Udemy - Online Courses - Learn Anything, On Your Schedule
Daily Coding Problem - Get exceptionally good at coding interviews
Code-Free Startup - Learn how to build real apps without coding
Takehome - Effective and humane coding challenges for candidates