The best alternatives to CheckiO are FINN.no, Kaboom, and Super Markup World. If these 3 options don't work for you, we've listed a few more alternatives below.
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Agree.com— Free e-signature for everyone with invoicing and payments!
Tech Roulette is a free game for the summer where you (and 500 students) get the chance to take a leap into fields of technology through a variety of random intro projects while earning rewards and prizes — all in your free time.
⭐ Programmable Robot with many Upgrade Parts ⭐ Real JavaScript Runner Engine ⭐ Programming Challenges (Missions and Story) ⭐ Smart Code Completion In Code Miner, you will be an engineer who have to program a mining robot for various, challenging tasks.