Plot of x^2+y^2 and related (for the slider graphs, select
the graph by clicking on it and then move the slider in the
toolbar)

wxdraw3d(surface_hide=true,
       enhanced3d=true,
       xlabel="x", ylabel="y", zlabel="z",
       title="x^2+y^2",
       line_width=1,
       zrange=[0,200],
       pic_width=700,
       pic_height=500,
       explicit(x^2+y^2, x,-10,10, y,-10,10),
       user_preamble="set xyplane at -11")$

with_slider_draw3d(
       a, makelist(i/2, i, -10, 10),
       surface_hide=true,
       enhanced3d=true,
       xlabel="x", ylabel="y", zlabel="z",
       title=concat("(x-(",string(a),"))^2+y^2"),
       line_width=1,
       zrange=[0,200],
       pic_width=700,
       pic_height=500,
       explicit((x-a)^2+y^2, x,-10,10, y,-10,10),
       user_preamble="set xyplane at -11")$

with_slider_draw3d(
       a, makelist(i*5, i, -10, 10),
       surface_hide=true,
       enhanced3d=true,
       xlabel="x", ylabel="y", zlabel="z",
       title=concat(string(a),"+x^2+y^2"),
       line_width=1,
       zrange=[-50,200],
       pic_width=700,
       pic_height=500,
       explicit(a+x^2+y^2, x,-10,10, y,-10,10),
       user_preamble="set xyplane at -65")$

with_slider_draw3d(
       a, makelist(i/5, i, -10, 10),
       surface_hide=true,
       enhanced3d=true,
       xlabel="x", ylabel="y", zlabel="z",
       title=concat("(",string(a),")(x^2+y^2)"),
       line_width=1,
       zrange=[-200,200],
       pic_width=700,
       pic_height=500,
       explicit(a*(x^2+y^2), x,-10,10, y,-10,10),
       user_preamble="set xyplane at -220")$

Here's a sliding trace

with_slider_draw3d(
       a, makelist(i/2, i, -10, 10),
       surface_hide=false,
       xlabel="x", ylabel="y", zlabel="z",
       line_width=1,
       explicit(sin(x+y)*(x-y), x,-5,5, y,-5,5),
       color=blue,
       nticks=50,
       line_width=4,
       pic_width=700,
       pic_height=500,
       parametric(t,a,sin(t+a)*(t-a),t,-5,5),
       line_width=2,
       color=green,
       points_joined=true,
       point_size=0,
       points([[-5,a,-9],[5,a,-9],[5,a,9],[-5,a,9],[-5,a,-9]]),
       color=black,
       label([concat("y=",string(a)),5,a,-9]),
       user_preamble="set xyplane at -11")$

Here are traces of the saddle x^2-y^2 (the odd way of plotting it seems to be because of bugs in wxmaxima or maxima)

with_slider_draw3d(
       a, makelist(i/2, i, -10, 10),
       surface_hide=false,
       xlabel="x", ylabel="y", zlabel="z",
       line_width=1,
       xu_grid=20,
       yv_grid=20,
       parametric_surface(x,-y,x^2-y^2,x,-5,5,y,-5,5),
       color=blue,
       nticks=50,
       line_width=4,
       pic_width=700,
       pic_height=500,
       parametric(t,a,t^2-a^2,t,-5,5),
       line_width=2,
       color=green,
       points_joined=true,
       point_size=0,
       points([[-5,a,-25],[5,a,-25],[5,a,25],[-5,a,25],[-5,a,-25]]),
       color=black,
       label([concat("y=",string(a)),5,a,-25]),
       user_preamble="set xyplane at -11")$

with_slider_draw3d(
       a, makelist(i/2, i, -10, 10),
       surface_hide=false,
       xlabel="x", ylabel="y", zlabel="z",
       line_width=1,
       xu_grid=20,
       yv_grid=20,
       parametric_surface(x,-y,x^2-y^2,x,-5,5,y,-5,5),
       color=blue,
       nticks=50,
       line_width=4,
       pic_width=700,
       pic_height=500,
       parametric(a,t,a^2-t^2,t,-5,5),
       line_width=2,
       color=green,
       points_joined=true,
       point_size=0,
       points([[a,-5,-25],[a,5,-25],[a,5,25],[a,-5,25],[a,-5,-25]]),
       color=black,
       label([concat("x=",string(a)),a,5,25]),
       user_preamble="set xyplane at -11")$

linear funcs

with_slider_draw3d(
       a, makelist(i, i, 1, 10),
       surface_hide=false,
       title=concat("1+x+(",string(a),")y"),
       xlabel="x", ylabel="y", zlabel="z",
       line_width=1, 
       zrange=[-40,40],
       explicit(1+x+a*y,x,-5,5,y,-5,5),
       pic_width=700,
       pic_height=500,
       user_preamble="set xyplane at -11")$

with_slider_draw3d(
       a, makelist(i/2, i, -10, 10),
       surface_hide=false,
       xlabel="x", ylabel="y", zlabel="z",
       line_width=1,
       xu_grid=20,
       yv_grid=20,
       title="1+x+3y",
       parametric_surface(x,y,1+x+3*y,x,-5,5,y,-5,5),
       color=blue,
       nticks=50,
       line_width=4,
       pic_width=700,
       pic_height=500,
       parametric(t,a,1+t+3*a,t,-5,5),
       line_width=2,
       color=green,
       points_joined=true,
       point_size=0,
       points([[-5,a,-25],[5,a,-25],[5,a,25],[-5,a,25],[-5,a,-25]]),
       color=black,
       label([concat("y=",string(a)),5,a,-25]),
       user_preamble="set xyplane at -11")$

with_slider_draw3d(
       a, makelist(i/2, i, -10, 10),
       surface_hide=false,
       xlabel="x", ylabel="y", zlabel="z",
       line_width=1,
       xu_grid=20,
       yv_grid=20,
       title="1+x+3y",
       parametric_surface(x,y,1+x+3*y,x,-5,5,y,-5,5),
       color=blue,
       nticks=50,
       line_width=4,
       pic_width=700,
       pic_height=500,
       parametric(a,t,1+a+3*t,t,-5,5),
       line_width=2,
       color=green,
       points_joined=true,
       point_size=0,
       points([[a,-5,-25],[a,5,-25],[a,5,25],[a,-5,25],[a,-5,-25]]),
       color=black,
       label([concat("x=",string(a)),a,5,25]),
       user_preamble="set xyplane at -11")$

one variable missing

wxdraw3d(enhanced3d=true,
         xlabel="x", ylabel="y", zlabel="z",
         title="z=x^2",
         pic_width=700,
         pic_height=500,
         explicit(x^2,x,-5,5,y,-5,5))$

wxdraw3d(enhanced3d=true,
         xlabel="x", ylabel="y", zlabel="z",
         title="z=y^3",
         pic_width=700,
         pic_height=500,
         explicit(y^3,x,-5,5,y,-5,5))$