Which platform is Cisco's SDN controller offering for enterprise connectivity?

Application Policy Infrastructure Controller - Enterprise Module (APIC-EM) is a Cisco SDN controller. This package is freely downloadable from the Cisco DevNet website as of this writing. It comes with several built-in apps, such as a plug-and-play module and a path trace module. Many other apps can be built on top of the APIC to extend functionality of the controller. However, the product has been largely replaced with Cisco DNA and is now licensed. OpenSDN is an open source SDN controller platform that utilized the open source OpenDaylight (ODL) protocol. OpenStack is another open source SDN controller aimed at data centers.