I'm teaching first-semester calculus right now, and I'm noticing that a lot of my students are using the online graphing calculator at desmos.com. (I think this sort of thing is like nuclear power, it can be used for good or for evil.) I played with the desmos app, and although it seems nice in some ways (human-like math notation, ease of use), in others it doesn't seem that great (e.g., you can't independently adjust the x and y scales, which makes it useless for some functions). I also feel that like is too short to waste time with proprietary software, so I spent some time trying to figure out whether or not desmos is open-source, and I couldn't find any info. (There appears to be a project of that name on github, but the README is uninformative, and I can't even tell easily if it's the same thing as the web-based calculator.) I've also used something called relplot: http://www.cs.cornell.edu/w8/~andru/relplot/ . It's cool because it can handle things like implicit functions and inequalities, and it can do ps and pdf output. However, it's not really open-source. (It's only free for noncommercial use.) Does anyone have any comments on whether there is a free and open-source web-based graphing calculator application that is best of breed?