BabelBrain is an open-source standalone graphic-user-interface application designed for studies of neuromodulation using transcranial ultrasound stimulation (TUS). It calculates the transmitted acoustic field in the brain tissue, taking into account the distortion effects caused by the skull barrier. The simulation is prepared using scans from magnetic resonance imaging (MRI) and, if available, computed tomography (CT) and zero-echo time MRI scans. It also calculates the thermal effects based on a given ultrasound regime, such as the total duration of exposure, the duty cycle, and acoustic intensity. The tool is designed to work in tandem with neuronavigation and visualization software, such as 3DSlicer. BabelBrain supports multiple GPU backends, including Metal, OpenCL, and CUDA, and works on all major operating systems, including Linux, macOS, and Windows. This tool is particularly optimized for Apple ARM64 systems, which are common in brain imaging research.