NASA Task Load Index (TLX) is an evaluation tool for measuring mental workload. It allows us to measure the mental workload of participants using VR systems while they are performing tasks in a VR environment. It examines task load across six dimensions
It has been cited cross various fields and evaluated systems ranging from military combat simulation to nuclear powerplant control rooms, etc. While it's utilized mostly for evaluating mental workload for interfaces involving physical components, "any interface experience requires some level of workload" can utilize the TLX.