I think of Outer like nikie's answer shows. Here's a similar view of Inner. Think of the arguments in columns. Apply f to each row and g to the result.

args = {{a, b, c}, {x, y, z}};
Format[g[e__]] := Column[{g, e},
   Dividers -> {None, {False, True, False}}, Alignment -> Center];
Inner[f, Sequence @@ args, g]

I think of Outer like nikie's answer shows. Here's a similar view of Inner. Think of the arguments in columns. Apply f to each row and g to the result.

args = {{a, b, c}, {x, y, z}};
Format[g[e__]] := Column[{g, e},
   Dividers -> {None, {False, True, False}}, Alignment -> Center];
Inner[f, Sequence @@ args, g]

I think of Outer like nikie's answer shows. Here's a similar view of Inner. Think of the arguments in columns. Apply f to each row and g to the result.

args = {{a, b, c}, {x, y, z}};
Format[g[e__]] := Column[{g, e},
   Dividers -> {None, {False, True, False}}, Alignment -> Center];
Format[f[e__]] := Row[{f, "@", e}, " "];
Inner[f, Sequence @@ args, g]

I think of Outer like nikie's answer shows. Here's a similar view of Inner. Think of the arguments in columns. Apply f to each row and g to the result.

args = {{a, b, c}, {x, y, z}};
Format[g[e__]] := Column[{g, e},
   Dividers -> {None, {False, True, False}}, Alignment -> Center];
Inner[f, Sequence @@ args, g]