Software to display 3D surfaces What are some examples of software or online services that can display surfaces that are defined implicitly (for example, the sphere $x^2 + y^2 + z^2 = 1$)?  Please add an example of usage (if not obvious).  
Also, I'm looking for the following (if any):  


*

*a possibility to draw many surfaces on the same sheet  

*to show cross-sections


I can’t comment eveywhere so I answer here :

I cannot display cylinder by ContourPlot3D[x^2+y^2==1,{x,-10,10},{y,-10,10},{z,-10,10}]. 

Try ContourPlot3D[x^2+y^2+z==1+z,{x,-1,1},{y,-1,1},{z,-10,10}] (see the result).
