I found this program while cruising the internet on the hunt for CNC info. What is most interesting is that it is a single file program with no installation needed. Looks like it would work well on older machines running older versions of windows. Best of all it is freeware and open source.

Here is a description of the software from the website;

SOLVESPACE is a parametric 3d CAD program. Applications include:

modeling 3d parts — draw with extrudes, revolves, and Boolean (union / difference) operations

modeling 2d parts — draw the part as a single section, and export DXF, PDF, SVG; use 3d assembly to verify fit

3d-printed parts — export the STL or other triangle mesh expected by most 3d printers

preparing CAM data — export 2d vector art for a waterjet machine or laser cutter; or generate STEP or STL, for import into third-party CAM software for machining

mechanism design — use the constraint solver to simulate planar or spatial linkages, with pin, ball, or slide joints

plane and solid geometry — replace hand-solved trigonometry and spreadsheets with a live dimensioned drawing

http://solvespace.com/index.pl

FEATURES

Sketch sections using

lines, rectangles, datum lines and points

circles, arcs of a circle, datum circles

cubic Bezier segments, C2 interpolating splines

text in a TrueType font, exportable as vectors

trims to split lines and curves where they intersect

tangent arcs, to fillet lines and curves

line styles for stroke color, stroke width, fill color

adjustable snap grid, for entities and text

menu item, keyboard shortcut, or toolbar

cut and paste, in plane and from workplane to workplane

background image with specified scale, for ease of tracing

3Dconnexion six degree of freedom controllers

Constraints and dimensions on

distance (or line length), point-line distance, diameter

projected distance, along a line or vector

angle, curve-to-curve tangency, parallel, perpendicular

horizontal, vertical

equal length, equal angle, equal radius, length ratio

line length equals arc length

point on line, point on circle, point on point, point on face

point at midpoint of line, line's midpoint on plane

points (or line) symmetric about line or plane

2d (projected into specified plane) and 3d geometry

lengths in metric or inch units

lengths entered as arithmetic expressions (32.6 + 5/25.4)

Build solid model with

extruded or lathed (solid of revolution) sketch

Boolean operations: union (add material), difference (remove material)

parametric step and repeat (pattern), rotating or translating

operations performed on either meshes or NURBS surfaces

Parametric and associative assembly

import parts and drag them with six degrees of freedom

import mirrored or with arbitrary scale

place parts in assembly using constraints

import surfaces, and merge them using Boolean operations

import lines and curves, for 2d work or solid operations later

changes in parts propagate automatically into assembly

Analyze with

measurements on a part or assembly (of point coordinates, line length, point-point distance, point-face distance, projected distance, face-face angle, point-line distance)

path traced by mechanism, exportable into a spreadsheet

area of a plane sketch, volume of a solid shell

degrees-of-freedom check to show unconstrained points in sketch

interference check for assemblies

"STL check" (vertex-to-vertex and not self-intersecting) for mesh

Export

2d vector drawing as DXF, EPS, PDF, SVG, HPGL, STEP

toolpath as G code

as either piecewise linear segments or exact curves

wireframe model, hidden-line removed model, vector shaded surfaces

isometric view, orthogonal view, user-specified other view

section of solid model

with cutter radius compensation

with adjustable canvas size

3d wireframe as DXF, STEP

triangle mesh as STL, Wavefront OBJ

NURBS surfaces as STEP

shaded view as bitmap