Shutterstock has very strict submission requirements for vectors that make it hard to use free software, for example, "no bitmaps" - saving gradients in Inkscape, for example, results in the bitmap problem. (Reference)
My ideal tool would be free (e.g. Not Illustrator) or low cost, and available on Mac, Linux, and windows if possible, although Android /iOS tablets seems reasonable too if it has standard vector features.
In other words: I am looking for a free (or not-so-expensive) alternative to Adobe Illustrator, which is able to export real vectors in a format that is compatible with Adobe Illustrator 10… including vector gradients-fills and co. Please note that Inkscape is not a valid alternative as it does not support the correct export of gradients-fills. Instead, Inkscape works around the problem by embedding a bitmap of the gradient, which is what I need to prevent to be able to upload my vector files to Shutterstock.