How many different charts does Billboard track?
Here they all are at Billboard’s web site.
A huge amount. Seems like sort of an obvious link to post so I do apologise but here is the list on Wikipedia: Billboard charts - Wikipedia, if you need the number them I guess you could count them.
Not only do they track lots and lots of different ones but the methodology of how they are compiled often differs from chart to chart as well. Even as a chart geek myself I still am astounded by how complicated and involved the whole thing is.