LeetCode - Practice and level up your development skills and prepare for technical interviews.
SmallDevTools - Handy developer tools with a delightful interface
Edabit - Learn to Code in 90 Days or Less
LaunchKit - Open Source - A popular suite of developer tools, now 100% open source.
Codewars - Achieve code mastery through challenge.
Profitable developer tools database - A database of 103+ hand-curated profitable developer tools