I think they use the same backend which is the steemit blockchain. the steemit UI and busy.org are just different front ends. one functional difference I've seen on other steemian accounts is they have a slider for how much percentage of their upvote they want to give. new accounts tend to default to 100% upvote . moving the slider down can spread your upvotes to more articles. I think other applications have a beneficiary like a small percentage of your earnings go towards the developers when using busy.org or dtube, I could be wrong. There's a reddit form of steemit, but I forgot whats it called, but it all connects to steemit blockchain rather than a small isolated ecosystem I think.