Please read the excellent dynamic essay project MorphLayoutArticle on Bob's SuperSwiki.
Every Morph now has the capability to layout it's submorphs. (Previously, only the AlignmentMorph could implement layout policies. Now AlignmentMorph is now deprecated, i.e., still in place and functioning, but not recommended for use in new code.)
You can find other layout methods under Morph->layout-properties. Also, play with a Morphs Layout Properties using the red halo menu. Here is some code to lay out some morphs in the new system.