Sam Ruby (prompted by Alf Eaton) combines Google Spreadsheets and Venus to let people manage Venus subscription lists (or whatever) using Spreadsheets. The lingua franca is of course CSV-over-HTTP. Like Unix pipes running over Internet, um, pipes.
Note that this requires the data to be publicly readable on the Spreadsheets side, which is fine for this use. A lot more uses would be enabled with a lingua franca for deputizing services to talk securely to each other.