Once the service provider is connected to the Fed (a somewhat complex process), it's normal software development. The client uses either MQI or JMS to send and receive messages; the messages are essentially ISO20022 XML. The development environment could be anything (any OS, any IDE). You interface those messages with your system of accounts. The Fed also provides a simple web UI and a testing network where you can test with other participants and run regression tests.
From a software development perspective, it's really quite normal.
From a software development perspective, it's really quite normal.