SNMP OID: .1.3.6.1.2.1.25.1.6 [for Unix, Linux, Windows as well as many other operating systems]
.iso.org.dod.internet.mgmt.mib-2.system.sysUpTime
Description: The number of process contexts currently loaded or running on this system.
 

WMI Class: Win32_PerfRawData_PerfOS_System
Property: Processes
Description: Number of processes in the computer at the time of data collection. This is an instantaneous count, not an average over the time interval. Each process represents a running program.