Personal Ancestral File (PAF)is by far the most popular genealogy and ancestry charting software, far more popular than gramps. When researching your genealogy at public libraries it would be especially nice to have your work on a thumb drive and be able to directly edit your PAF file while on the library's computer. I know it's not open source, but the LDS church (which owns it) might be interested in making a portable version for the reason I stated above.