This article presents RT-AIDE, a real-time operating system (RTOS) Agnostic development environment considering performance evaluation and interoperation with nonreal-time tasks. Most real-time systems adopt RTOSes owing to their multitasking environment and priority-based scheduling. However, selecting for the appropriate RTOS according to application requirements is a complicated process as each RTOS has its own API and semantics. With open-source distributions real-time performance evaluation is also an open problem. RT-AIDE addresses this issue through the portable components to ensure execution across various RTOSes without modifying the source code, which has been proven to reduce development costs and effort as well. We also propose a new metric called real-time performance index to evaluate the behavior of the running application. To validate feasibility, theoretical analysis and practical experiment has been conducted on an actual control system based on Xenomai and RT-Preempt.