Obviously, one for personal stats.
My industrial league has old guys who keep stats and got someone to launch a website. It actually calcs OBP/OPS/SLG etc..... You can click on a name and it shows you a breakdown by game for any player. Completely unexpected and very cool.
Of course, now that this is out there, it will now lead to irrational agitation when a line drive that nicks the second baseman's outstetched glove is ruled an error, or when two of your doubles get put in as singles. Just speculating what
might happen, of course.