The application is still there, but in your site it has been renamed to "Notes & Queries".
This is an oddity of the Applications list - if you rename an application (to give it a name more suitable for your site) then it uses this name in the list of applications.
So you can enable "Notes & Queries" and, if you like, rename it to "Weblog" or something like that!
Note that the "Noticeboard" application is basically the same as Weblog too. So if you want to have two for different purposes then you can.