This is a replacement for the Integrated Circuits that used to be readily available. While the LM13700 is still being made, but who knows for how long. Many other parts have disapeared and the OTA is one of the primary building blocks of an Analog Synthesizer. This is an open source project, however, the tools I use are not. :( Still, I will make the cad files available as well as the cam files. I plan to get the boards made on OSH-PARK so you will be able to order them from there. This will all take place hopefully by early January 2016.