FASTchip //e from a2heaven.com preview sample copy preview now at :
It's low energy consuming Accelerator card for Apple //-series with acceleration from 0 to 16.6Mhz. You can stop the CPU, or by using rotary knob, adjust the CPU to run almost any frequincy from 0 to 16.6Mhz! This is very very handy.
Current development version works in Apple //e but soon in Platinum //e and ][+ as well.
Not yet available but should be in summer-fall of 2017 for 150 dollars shipped everywhere from http://a2heaven.com