I could build this non exhaustive list of RTOS : VxWorks, QNX, LynxOS, eCOS, WindowsCE, LinuxRT, Micrium, PURE, MMLite, XPembedded, RTAI, xenomai, Integrity, Nucleus, ThreadX.
From what I know, probably WxWorks and LynxOS are the best choice when security is required (ISO 15408). On the other hand, I worked recently on a Linux setup with "PREEMPT RT" set in the kernel for an embedded system. This setup had signed boot-loader, kernel, system and applications, with cryptographic keys in a TPM. Ok, this is just to provide you the context and where I am in my research.
My question is : Is there a recent survey of RTOS solutions, security centric ? Alternatively, what are your choices, why and for which usage?