I made a table-top instron to measure milli-newton forces.
I'm using a micrometer stage that we had lying around and just machined an adaptor to attach a stepper motor to the end.

The load cell is scavenged from a low cost jewelry scale which has a range of 20g and an advertised resolution of 1mg.
By using a 24-bit ADC and amplifier (TI ADS1231) along with oversampling 16x and decimating (see this nice app note), I can achieve better than 10mg resolution (noise is on the order of 1mg).

To interface with the hardware, I built a javascript/node interface. This is essentially a fancy serial monitor that enables commands to be sent to the machine, read data back, and plot it.

I'm using this machine to characterize the stiffness of small-scale flexural mechanisms, as well as the force output from electromagnetic actuators.