In Brief
This isn't a new widget per se, so much as a convenient automatic alias to the Tk scrollbar (on Mac) or Ttk/Tile scrollbar (elsewhere).
At the time of writing (Tile 0.7.8, 0.8.2), Tile/Ttk's 'Aqua' theme's scrollbar seems more like it's from the 'Default' theme. The Tk scrollbar is far and away more platform native.
Commands
::tclmacbag::scrollbar pathName ?Options?
Available options:
See the Tile/Ttk scrollbar and the Tk scrollbar documentation. These widgets share the same commands and options for navigation and control.
However, if you're doing anything unusual, you should compare the two commands and check to see that what you want to do is supported by both.
Example
grid [text .sf -yscrollcommand {.vs set}] -row 1 -column 1 -sticky nsew
grid [::tclmacbag::scrollbar .vs -orient vertical -command {.sf yview}] -row 1 -column 2 -sticky nse