Robert Walker aka ten_foot published his Eskarp – a handwired split with TPS65 touchpad.
Added a TPS65 touchpad from Azoteq to my eskarp keyboard – ten_foot.
TPS65 touchpad
The optional touchpad is the TPS65-201A-S from Azoteq which appears as a USB HID mouse to the host computer.
As janaka1 points out, the Azoteq touchpads are "cheaper, more sensitive and more readily available" compared to the popular Cirque trackpads:
I am building an ergonomic keyboard with a trackpad using Azoteq proxsense TPS43 and TPS65 trackpad modules. […] These trackpad modules are bigger than the biggest Cirque Glidepoint modules that are commonly used by the ergo keyboard community. Yet they are cheaper, more sensitive and more readily available in both Mouser and Digikey – janaka1.