Whitebox switches represent a new category of switches that were brought to mass market by the SDN movement. They represent a class of switches that typically made by vendors who made network hardware as outsourcers for the typical commercial vendors such as Cisco. Since the SDN movement allows network engineers to only care about 'raw' forwarding plane, the whitebox switch vendors can now sell directly to the network engineers. They are just blank switches upon which you can load separate software for them to operate on. The hardware vendors include Accton, Celestica, and Quanta, amongst others.
The software you can load on the switch varies from just an agent interacting with controller, such as Big Switch Networks Switch Light OS, to standalone full-feature operating system, such as Pica8 and Cumulus Linux. This is an area that is quickly evolving and offers no shortage of innovation. The following outputs show a relatively old Quanta LB9 switch running Pica8 PicOS 2.8.1. The software offers different modes, such as OpenFlow native or hybrid mode, where the port follows the normal L2/L3 pipeline for flow-miss.

XorPlus login: admin 
Password: 
admin@XorPlus$

admin@XorPlus$cli 
Synchronizing configuration...OK.Pica8 PicOS Version 2.8.1 
 
Welcome to PicOS on XorPlus 
admin@XorPlus>

admin@XorPlus> show version
Copyright (C) 2009-2017 Pica8, Inc.
===================================
Base ethernet MAC Address : <skip>
Hardware Model : P3295
Linux System Version/Revision : 2.8.1/f2806cd
Linux System Released Date : 01/04/2017
L2/L3 Version/Revision : 2.8.1/f2806cd
L2/L3 Released Date : 01/04/2017

admin@XorPlus>

Can you tell it was a Quanta LB9 switch? No, which is the point. Pica8 software or other software will run the same on all whitebox switches. This category of switches represents the true potential of SDN and the closest that we have seen of a decoupled future of network hardware and software.