from the official steemitblog:

Multiple Arbitrary Beneficiaries to Reward Payouts

For any given post there can be a half-dozen different people who have a financial interest in the reward. The include: voters, author, referrers, hosting providers, blogs that embedded blockchain comments, and tool developers. Whatever website or tool that is used to construct a post or comment will have the power to set how rewards from that comment are divided among various parties.

This means that if you post via Busy.org that your post will share some of its rewards with Busy. If you post through the various phone and/or desktop apps then the app developer will be able to claim some of the rewards.