What operating systems does LingTree run on?

Windows, Mac OS X, and Linux operating systems

What graphic formats does LingTree save the diagram in?

PNG, and/or SVG.

How do I indicate what graphic formats I want LingTree to save the diagram in?

Use File menu item / Save tree as .png and/or Save tree as .svg.

How do I indicate a node is a lexical item?

Type \L before the lexical item.

How do I indicate a node is a gloss item?

Type \G before the gloss item.

How do I indicate a node should have a triangle over it instead of a vertical line?

Type \T before the item.

How do I indicate a node should not have a vertical line or triangle over it?

Type \O before the item.

How do I indicate a part of a node is a subscript?

Type /s before the subscript.

How do I indicate a part of a node is a superscript?

Type /S before the superscript.

Can I have both a subscript and a superscript showing one over the other?

Yes.

How do I set the fonts for nodes, lexical items, and glosses?

Use Format menu item / Non-terminal font or Lexical font or Gloss font or Empty element font.

Can I have curved lines or arrows in the diagram?

No, sorry, not with LingTree.  You can, however, save the basic diagram as an SVG file and then use a tool like Inkscape to add the curved lines and arrows.