DFD Geth JSON is a LAMP-based web application aimed at providing a complete toolkit for interacting with the Ethereum blockchain, using the geth p2p node / client software via JSON-RPC. It lets you perform JSON-RPC requests to your local network Geth nodes. You can create contracts, transfer / view balances, see network / mining status, and more.
Please be sure to read the security infomation related to safely running this application, or you risk the possibility of losing funds from your account. This application is currently only intended for usage across your local network, opening up RPC ports to the external world wide web is not recommended and is a high security risk, see this alert posted by the Ethereum developers on this particular topic.
NOTE: This is still a very early Alpha release, see the milestone tracking page for more details on what is planned and what is completed.