Either the service is just funneling money to software authors, or they are collecting it themselves and holding it unless and until authors want it. So if it's the latter, then they are raising money using someone else's name and reputation. Either way, that's not at all cool.
First, the money isn't available since it hasn't even been sent to you. Until you sign-up for the service, and provide a bitcoin address for the funds to be sent to your private key, they are not available. But more importantly, since you have no business relationship with the person giving the money, I would think the best characterization for the income is a tax-free gift (up to $14,000 per giver). But IANAL, and this isn't tax advice.