Inkscape is an open source app which you can use for converting SVG files (like favicons) to PNG. Modern browsers support favicons in SVG format, though mobile devices prefer PNG files in particular sizes. You can use Inkscape from the command line to convert an SVG to PNG: `inkscape -h 192 input.svg --export-filename output.png`. Here, the “-h” flag specifies the PNG file height in pixels. Once you have generated the PNG, you can optimize with another open source tool: OptiPNG. As with Inkscape, you can run from the Terminal `optipng -o7 -out optimize.png output.png`.