The Projection Toolbar created by Didier Bur on SketchUcation.com is a simple toolbar that allows you to create projections from points, lines, or faces. Some of the tools from the toolbar are more useful than others.
A very useful tool from these sets is the 4th tool, “Project lines perpendicularly to a face” and the 5th tool “Project lines perpendicularly to a faces”, it projects a line segment down to a face. Normally to do this you would have to copy the line segment down and then connect all the edges to create the faces. Another one is the 8th tool, “Create lines at intersections of selected faces”, this creates construction lines at all points of intersection of a selected object. Works great when you need to use those lines as references for other objects.
The 9th and 10th tool allow you to “push pull selected faces along a vector” and “push pull selected faces along their normals” these are great to extrude the surfaces out but it can be fairly buggy. There is another plugin that allows you to do this type of extrusion and has less issues with the extrusion, it is the Joint Push Pull Plugin.
The other tools let you do simple projections. The 1st tool allows you to create a simple construction point. The 2nd tool allows you to project that point to a line, this tool is not as necessary as you can do this simply by just creating a line from the point to the surface. The 3rd is similar to the second but projects the point to the surface. The 6th and 7th allow you to extrude a surface down. The 6th tool only allows you to project downward (like the regular push/pull tool) and the 7th tool allows you to project the face on an angle (by vector).
Overall, the Projection Toolbar created by Didier Bur is a good toolbar to help you project lines and surfaces onto other surfaces. At the time of this review this plugin is free and is available at SketchUcation.com. I give this plugin 3.5 out 5 stars.