I've had an idea to build a list app for a while, but the devil is in the details.

My mental list (ahem!) of features went like this:

- It needs to hold lists of key/value pairs of any size (bit like memcached, or a list of dicts in python)

- It needs to have RPC access to add/insert/delete/update keys and values

- There needs to be pub/sub access to the RPC interface, replication needs to be instant, and it needs to be able to advise you if the replication is degraded. Some sort of MQ service.

- It needs to have client libraries in a few languages, and some example apps

- It needs to have a web front-end for inspecting and managing lists and permissions

Imagine the possibilities!

- you could have a desktop/web and iphone app that monitored stock prices, your server status, or other arbitrary figures

- you and your wife could have the ultimate shopping list (delete butter on one and it's instantly gone and deleted on all devices - fantastically useful)

- you could re-invent irc

- you could make hypertwitter 2.0

- you could make a message queue service

- you could build a CDN or cache on it.

Has this been done? I know Google Spreadsheets is about 5% of the way there.