Ripple is a real time gross settlement system (RTGS), currency exchange and remittance network. Used by companies such as Santander, Unicredit and UBS. More than 17 banks are using it.
Make all participants to share and create a new cryptocurrency for the financial sector was the idea, and this this has become Ripple afterwards. Digital Asset Holdings has built a module to setup public or private chains depending on the wishes of the customer and collaborate with existing financial applications.
Interledger is the protocol that sits under RippleNet. Being developed as a potential web standard under the watchful eye of the W3C. Used to join the ledgers of banks together into a network, and could be used to join XRP or any other ledgers together. Its not only open source but on its way to become a web standard (or part of one), so it can be incorporated into browsers.