ONOS was conceived and produced by ON.Lab with support from AT&T and NTT. ONOS later became a project of the Linux Foundation (LF) where it lives today. ONOS is meant to operate as a cluster, which is different than OpenDaylight which was designed to be run as a single system:
ONOS controller
The ONOS controller differs from OpenDaylight in how it handles clustering multiple controllers. In the preceding figure, you can see that there are 300 devices, spread across two controllers, 150 each.