I'm thinking about a mod to display in a portal island, or better yet, as part of forum statistics portal, the # of users that have been active over some configurable period of time. Even better would be to have it display possibly 3 periods of time, for instance, the # of active users over the past day, week, month.

To define active user, I'm thinking ostensibly of those who've logged in in that time period. Another variant or a modification to this theme would be # who've posted over those time frames.

To wrap that up with a nice bow, even to have an option of expressing that # as a percentage of your total user base. Also, some ability to possibly display right in your face (rather than have to do the math yourself) the percentage of active posters against the overall logging in base on those same time periods.