Advanced Normalization Tools is a suite of tools for “spatial normalization” or warping or registration. Like fsl's flirt/fnirt or AFNI's 3dQwarp. (NB. resample like 3dresample is not warping).
Among many other pipelines, ANTs is used by fmriprep to align per visit T1w images to the MNI template creating non-linear warp files like sub-10644_from-T1w_to-MNI152NLin2009cAsym_mode-image_xfm.h5