ATI Nucleus PLUS

Nucleus PLUS is a real-time operating system (RTOS) developed by ATI in 1993. Many Agere Samsung and TI Calypso LG feature phones used proprietary operating systems based on Nucleus PLUS.

MediaTek's proprietary OS is based on Nucleus RTOS as well.

If a phone uses Nucleus as an RTOS, the version can be found by analyzing copyright strings in a phone's firmware image (binwalk can do this)