Working with surface data in R
See Val's tutorial on github https://github.com/PennLINC/surfaces_R_tutorial/blob/main/surface_tools_R.Rmd which covers information about cifti files and the fslr surface, types of ciftis/giftis, and how to read, manipulate, write, and visualize dense and parcellated cortical surface data in R
Working with surface data using Connectome Workbench
Connectome workbench has a ton of tools for working with surface data and cifti files. See all of the available workbench commands here https://www.humanconnectome.org/software/workbench-command/-cifti-create-dense-timeseries
Connectome wb_view is a GUI for visualization surface data, which can be downloaded here https://www.humanconnectome.org/software/get-connectome-workbench. To visualize surface data in workbench, you must load a .surf.gii surface geometry first, and then your surface data