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Convert is a freeware utility that will convert one unit of measurement, such as distance, temperature, volume, time, speed, mass, power, density, pressure, and energy, to another. It's available for both Windows and Linux. It also doesn't require any installation, so you just have to unzip it to use it on a PC.

Some links are broken and I know of some good software that is missing from this list, but this is still a nice list of useful links and it includes a lot of freeware. This might be a good place to start if you're looking for CAD/CAM/CNC programs.

Paul Bussieres' free Visual Basic calculator for the mini-lathe will calculate gear combinations for a metric or English leadscrew. Simply specify the desired pitch and it will produce a list of gear combinations that will work. If you have trouble understanding the gear diagram then look at the gear chart located on your lathe or in your manual. This program has a French and English interface.

ME Consultant is a collection of machining calculators and data tables with a graphical interface. It will calculate cutting speeds for different materials for drills, end mills, lathes, reamers and many other cutting tools. It also has data tables for threading, drill sizes, hardness and more. This utility also doesn't any installation. Just unzip it and run it.

Alan J Munday created this very useful, FREE, easy to use, suite of calculators and information for machinists and engineers. There's too much to list here, but it includes a cutting speed and feed calculator that is one of the best we've seen. It also includes thread cutting data, a spring designer, a unit converter, information for setting up tapers, a sine bar and gauge block calculator, sheet metal bending information and calculator, a gear cutting calculator, and MUCH more. Both metric and English units are supported. This is the core program and there is an upgrade that adds even more capabilities to it.

This is an online utility. Choose the type and style of graph paper you want, the grid size, and size of the paper you want to print it on. It then generates a PDF file that you can save or print out. Supports both inch and metric units.