How could one make a site like donationcoder enabling donations with bitcoins ?
For example a download site for homebrew game developers which allowed payments / donations whenever someone downloads digital productions
The simplest way would be to just show an address, either in plain text or as a QR code. People scan the code in their wallet application, send, done: bitcoins are delivered.
Blockchain.info offer a simple donation button maker, ready to be cut & pasted on a web page, that generate a different address every time (to complicate things a bit to whom want to try to see how much bitcoins the receiver have accumulated) and display a QR code.
Or, a payment processor like BitPay can be used, to let users pay in bitcoins and receive the corresponding amount in the legal tender of choice, with a minimal fee (1% per transaction or fixed 30$ monthly, if I remember correctly).