Oddball Plugin Request

OKay, this is something I could probably hack up using PHP and MySQL, but I thought maybe someone else had already done it and I just don’t know what to call it.

I’m looking for, I suppose, a “private shoutbox”. That is, a shoutbox-type app that only I (the site admin) can post to.

The purpose of this is for little brief newslets. I’d like something where I could input things like “Happy Birthday Anne”, “Now Reading: Perdido Street Station”, “Bah, more snow”, things like that. It would date/timestamp each entry, and scroll older ones off after a while.

I know this sounds dumb, but I figure someone else might have wanted something like it at one time. Does anyone know of such a plugin that already exists, or do I need to learn how to write one of my own?

Thanks!