At right is a picture of the the "jellyfish" version of the NTRC-A Model Train Controller. The User and Service Manual is available in PDF format.
Below you see the B-model, identical except for the absence of the Thrust-Brake control and the inputs for layout automation, but in exchange being very compact and easy to manufacture, by virtue of assembly of the PCB in a shell without further wiring.
This controller has a long list of features, but is chiefly distinguished by achieving feedback speed regulation without using any Pulse-Width Modulation (PWM). It uses an adaptive-control with negative-resistance technology to regulate speed without needing to pulse the power on and off. It is thus very gentle on small armatures. The technology is reported in a journal paper, accessible here. Design details are in the srvice section of the User and Service Manual.