Here's a related idea: Someone should start a very large Redis instance, say 8GB of RAM on an EC2 node, with shared reads (i.e., all clients can read all keys),

Here's a related idea: Someone should start a very large Redis instance, say 8GB of RAM on an EC2 node, with shared reads (i.e., all clients can read all keys), but protected updates. Each app would use a prefix on its keys. This could be used as an open message passing bus between apps that need to communicate.