Free software to draw Newman projections
You can use GChemPaint, which is available on the repositories of many popular distributions. Among its many components for drawing structures, it has a specific tool for Newman's projections.
You can add H, O and many other elements by simply right-clicking on the molecule, and it even allows you to search your molecule in databases like PubChem and ChemSpider.
A useful video tutorial can be found in spokentutorial.org

3.11 To Add a Newman Projection
To add a Newman projection, use the following tool:

This tool allows to add a Newman projection. The changes become permanent only when the mouse button is released.
To add a Newman projection, click on the background. Contrarily to other tools existing atoms are never used by this tool. It creates new atoms of the current element.
When the Newman projection tool is active, the toolbox looks like:

Options for the main bond

Bond length
The default length of the new projected bond. This has no influence ion the drawing, but might be important when exporting to a 3d model.

Bond order
The bond order.


Options for each atom

Bonds number
Number of other bonds for the atom.

First bond angle
The direction of the first bond. Angles are measured counter clockwise from horizontal right.

Angle between bonds
The angle between two consecutive bonds.


Warning
This version of GChemPaint does not correctly support Newman projections with eclipsed bonds.


Source: GChemPaint manual, pages 41-43.