Pretty much all the embedded devices are powered by different firmwares depending on the complexities. Heavy task performing embedded systems would definitely need a full operating system such as Linux or Windows NT. The following provides a non-exhaustive list of operating systems that are normally found during firmware analysis:

• Ambarella: An embedded operating system mostly used in video cameras, drones, and so on.
• Cisco IOS: Cisco's Internet Operating System.
• DOS: A disk operating system that is considered obsolete. But testers never know what they find during an assessment.
• eCos: Embedded Configurable Operating System, open source real-time operating system by eCos community.
• JunOS: Juniper Network System—Juniper's custom operating system based on FreeBSD for its router devices.
• L4 microkernel family: These are second-generation microkernels that will look like Unix-like operating systems.
• VxWorks /Wind River: A popular proprietary real-time operating system.
• Windows CE/NT: Microsoft-enabled embedded compact devices, very rare to find on a device.