Linux:
ps
The ps command lists running processes. The following command lists all processes running on your system:
ps -A
If this is too many processes to read at one time, you can pipe the output through the less command to scroll through them at your own pace:
ps -A | less
You could also pipe the output through grep to search for a specific process without using any other commands. The following command would search for the Firefox process:
ps -A | grep firefox