I'd like to have a server app that provides a messaging service between the clients. There a few different sort of things I'd like to do:



- When certain fields are updated on a certain BO, it changes the application state. Rather than code to errors (because another user attempts something that was legal when it retrieved the state, but the state has now changed), I'd like to be able to just notify the clients so they can get the new state and adjust to it.



- For administration purposes, it would be good to know who is on, in real time. The way chat clients can show a list of friends online is what got me thinking about doing something chat like (though I don't intend to allow users to chat, just the client apps).



- For both administration and security purposes, I'd like to be able to kick off users, send out notifications etc. in real time. This would be used when the app is being upgraded, to make sure no one is on (and give them a 10 min warning). For security, in case we have a particularly naughty user, I could kick them off immediately.



I'm just a total newbie at doing anything like this. I've done a bit of research on using network streams, but don't know where to start. I'm also wondering how I'd do this if I were to use IIS and an ASPX page. I'm not sure that would work because I'd need to have a client talk to the server, which would broadcast to other clients.



Any help/starting tips would greatly appreciated!



Thanks!