Talking about WebMoney, there are some different interfaces, the simplest of them is here and here is the list all of them. The second most popular of the Russian gateway is Yandex.Money (link goes to an API). Also there is an aggregator of all major payment systems in Russia - Robokassa (link goes to an API as well) it is support WebMoney, QIWI, Yandex.Money, Visa/Mastercard and so on in one interface.