This is an Eight slot FeatherWing connector board with a ninth controller slot.
Each slot is connected to the next allowing you to stack up to 8 featherboards together. Each slots EN and NC pin is routed to the 9th slot to allow individual control of the EN's of each feather and the NC can be used as a Interrupt pin for individual interrupts routed from each board.
Note: Slot 9 has 16 of the Feather pins rerouted to the other slots. However the I2C, Serial and Power are in the same format.
The Octo board has mounting for each feather but the hole sizes are slightly larger allowing to fit a more common found M3 bolt instead of the original M2.5 bolts found on a standard feather board.
You will need to solder the sockets or can solder the FeatherWings directly for a more permanent solution.
There is a pre-solder option available.