For drawing arrows, I use drawing toolbar of LibreOffice Writer. For vector graphics, and converting bitmap to vectors, I use Inkscape. For flowcharts, I use

For drawing arrows, I use drawing toolbar of LibreOffice Writer. For vector graphics, and converting bitmap to vectors, I use Inkscape. For flowcharts, I use Dia. For bitmap graphics, I use Gimp, use it for crop and prettifying old photos. I use OpenClipart SVG images, when I need some image that is already made.