Currently, in the worst possible way, Roblox. I hate everything about their business model but the environment is perfect for encouraging programming. For start

Currently, in the worst possible way, Roblox. I hate everything about their business model but the environment is perfect for encouraging programming. For starters, developers/hackers are often represented as heroes. Kids know who they are because they're the subject of in-game lore and YouTubers talk about them a lot. Second, Roblox Studio is a mostly complete, easy to work with game making environment, assets are easy to obtain and scripting is in Lua. Most importantly, kids can show off their work immediately to all of their friends in a multi-player world. The bad parts of Roblox provide an opportunity for me to explain exactly what's bad about proprietary tools, centralization, pay-to-win, spending real money on digital goods, etc. Roblox isn't much worse than AAA games in this regard. My kid is showing forethought about spending his limited supply of Robux and he's parroting some of my rants when he talks himself out of buying something. Hopefully that parroting turns into genuine understanding. Eventually, he'll want to move on from Roblox or they'll disappear and he'll learn first-hand the pain of moving to a new platform and leaving all of your code and digital goods behind; and that the only things that last are libre code/assets, algorithms, concepts, ideas and memories.