scatterplot.online is described as 'tool for quickly creating scatter plots from data in the browser. No account, no login required. Just drag and drop csv file or copy paste it into the page and you will see your diagram in a matter of seconds'. There are six alternatives to scatterplot.online, not only websites but also apps for a variety of platforms, including Mac, Windows, Linux and Self-Hosted solutions. The best alternative is Tableau. It's not free, so if you're looking for a free alternative, you could try RAWGraphs or Plotly. Other great sites and apps similar to scatterplot.online are Marple (Free), LightCat (Free) and AnswerMiner (Freemium).
RAWGraphs is an open source app built with the goal of making the visualization of complex data easy for everyone. Born as tool for designers and vis geeks, RAWGraphs aims at providing a missing link between spreadsheets and vector graphics editors.