Hi @JustinZ, if you have an existing Rhino toolbar, have you tried to script the command PopUpToolBar followed by the toolbar name ?
Alternatively, if you know how to create an Eto.Forms.Dialog, you could get the mouse position and open the dialog at this location. If you set the WindowStyle of your dialog to Eto.Forms.WindowStyle.None you could make it appear like a toolbar. You then need to close the dialog once one of the buttons is clicked or if nothing was clicked. @dale posted a cool example here which shows a row of toolbar buttons in a dialog.
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c.