PayPal announced its Adaptive Payments API yesterday (11/3/09). This new API allows two complex payment types — Parallel and Chained payments — in addition to the usual one sender, one receiver transaction. The parallel payments option splits a single payment to up to 6 separate receivers. Chained payments allow for one primary receiver and up to 5 secondary receivers. For parallel payments, the sender pays each receiver directly. For chained payments, the sender is only aware of the primary receiver, the chained payments receivers are never revealed to the sender.
There are also other features such as PayPal registration and currency conversion support in the new API. Read more about it –
PayPal X: PayPal X Adaptive Payments API