The Compute Module 3+ Dev Kit is for those who wish to make use of the Raspberry Pi in a more flexible form factor, intended for industrial applications. The IO Board V3+ is made for developing with CM3+, CM3+/Lite, CM3, CM3L, and CM1.
The accompanying IO Board is a simple, open-source breakout board that you can plug a Compute Module into. The board hosts 120 GPIO pins, an HDMI port, a USB port, two camera ports, and two display ports. Designing the Module into a custom system should be relatively straightforward as the Raspberry Pi Foundation has put all the tricky bits onto the Module itself, and you have the freedom to add extra components and place parts exactly where your product needs them.
Once you've got your design and peripherals chosen for use, you can take the I/O board design files, remove all the components you aren't using, and get the perfect Pi design for the Compute Module!