https://awwapp.com free version has some limitations, among others, no save, just export to PDF with watermark and no multipage, and a bit disturbing add banner at the bottom
drawing, typing, moving objects etc, very comfortable
pointing visible - users may point on objects, the other can see
BigBlueButton offers shared board. You can either draw to the uploaded PDF presentation or used the default one - go to next page. All-drawing can be anabled by using the menu on right.