We're not free, but MotiveWave has low cost editions, depending on what features you need. If you only need charting (no trading), our basic Charts Edition is $99 for a lifetime license. You can see more info here: https://www.motivewave.com/products/charts-edition.htm
I use thinkorswim and its a very nice charting. It has other little capabilities that I find useful. For example you can color code your chart windows and your stock list window and others like the analyze tab, options window etc and with one click of the ticker symbol, all windows will update to the stock of interest. You can line up charts with all kinds of studies and do your observations with just one update of the ticker symbol on anyone of the windows.