Unreal
Unreal is at its core, a game engine created by Epic Games but it has a large swath of applications in the live performance industry. Unreal offers an excellent real-time 3D environment that can create stunning visuals without rendering. Programming can be done either with its built-in nodes or directly in C++. It is capable of releasing on most modern gaming and VR systems as well as Windows, macOS, Linux, iOS, and Android.
Unreal is used extensively in virtual production pipelines and can be connected to either professional tracking gear or more consumer-grade options such as the HTC Vive.
There are substantial assets available both paid or for free available on the Epic Marketplace and the engine comes with example content built into it.
While there are many great tutorials available online (both from Epic and from the creator community) Unreal has a fairly steep learning curve and requires pretty hefty computer resources to run.
COST: Free until a project makes 1 million dollars in gross lifetime revenue