Calculator similar to Desmos but for $3$D Is there a calculator with functionality similar to Desmos but in $3$ dimensions?  I am looking to learn about families of quadric surfaces so I am looking for a $3$D calculator with sliders.
 A: If you are on a Mac, you can try the included application called Grapher:


*

*Open Grapher by opening Spotlight (Command+Space) and typing 'Grapher' (and hitting enter)

*Click '3D Graph' and hit the Choose button

*Your text cursor should be to the right of 'z=' inside a text box; type any 3D function including the parameter 'a', such as sin(a*x), and hit enter

*Click the plus button at the bottom left hand corner of the window, and click New Equation

*Erase the 'z=', type 'a=2', and hit enter

*Open the Equation menu and select Animate Parameter

*Now drag the slider to change the parameter!

*(optional) If you want to have the slider act continuously, click the right most 'Settings' button above the slider (with the two checkboxes and lines), and check the box labeled Continuous Range


Enjoy!
A: You can actually just use Desmos!
https://www.desmos.com/calculator/euncwbhqlb
A: Updated, December 2018: I made the following website with the aim of producing a Desmos-like experience in 3D for my multivariable calculus students.
math3d.org
You can create and animate points, vectors, curves, surfaces (explicit & implicit), and vector fields. After creating a demonstration, you can save it and share.
Here are three scenes that I particularly like:


*

*Parametric Curves, Velocity and Acceleration

*Volumes of Revolution, Shell Method

*Hyperboloids as a Ruled Surface (+screenshot) 
This project is on Github. If you find bugs or have ideas for improvements, please open an issue!
A: http://www.graphycalc.com/ is an excellent site. try it out.
A: GeoGebra does exactly what you want:
https://www.geogebra.org/3d
It already supports all quadrics. You can try it here:
https://www.geogebra.org/3d?command=a=1;z=x%5E2-a*y%5E2#3d
A: You might try http://web.monroecc.edu/manila/webfiles/calcNSF/JavaCode/CalcPlot3D.htm.  It has sliders available under the Parameters->Adjust Parameters menu option.
A: This is nice too. Try it out https://www.geogebra.org/3d?lang=en  :) 
A: Just about all of the 3D plotters I've seen online fail in a few major areas:

*

*Asymptotes. For example, $f(x,y) = \tan(x)$ shouldn't have vertical planes in its graph.

*Plot boundaries. Functions with restricted domains, i.e. $f(x,y)=\sqrt{1-x^2-y^2}$, should not have jagged triangles where the domain ends (in this case the unit circle on the $xy$ plane).

*Discontinuities. Related to #1, but also applies to step functions and the like. Discontinuities should not be visible as an abrupt vertical plane.

Awhile ago I attempted to address these issues in Koval's 3D Grapher. Now at the time I wasn't nearly as clever as I really needed to be, so it still struggles with some things (notably $f(x,y)=\tan(x)+\tan(y)$ and other "2D asymptotes"), but in general it does pretty well:

Also supports spherical and cylindrical coordinates and some 1D and 2D parameterized graphs.
