A commercially available product: TurboBrainVoyager
Freeware: OpenNFT
(Matlab and Python based toolbox for ROI, MVPA and DCM connectivity feedback)
(for details see Koush et al., 2017, NeuroImage)
Freeware: AFNI (by using the AFNI plugin "plug_realtime")
Freeware: Friend
Freeware: BART
Freeware: scanSTAT
Freeware: fieldtrip