Moldable/Printable wood-like material? I like the look and feel of wood, and it is structurally strong, suitable for architecture and furniture-making. 

However, to make odd shapes, different from typical woodshop cuts, it either involves more specialized tools, such as lathes and routers, or carving, which involves a lot of skill and waste. 

Suppose my projects is a piece of furniture where part of it looks like tree roots, but it is a set of roots that I designed, rather than one I found. It would be very hard to make in a traditional wood shop.

If I wanted to have a wood-like object, either from a 3-D printed master or a mold, are there materials that I could use in that way, that look and act like wood?
A quick search of the grand ol' internet shows that most people are recommending a wood fiber filler to be added to traditional casting material such as epoxy or polyester resin. There is a PDF available showing how to combine pecan shell flour(!) with resin and post-processing in order to generate a wood grain surface.

My search results provided a link to an Instructables comment/query with a link to the PDF noted above. I've provided the link to that page rather than the PDF, as some of the comments may also be helpful to you. The first link provided in the Instructables article is 404, dead and gone but the second one is still operational.

The document in PDF form is now a direct link and references a specific product, Smooth-on 320 resin, likely a product sold by the site hosting the document. 

The results of my search which were the most promising also referenced pecal shell flour or powder.

I suspect you will get wood-like appearance, but not necessarily wood-grain like appearance.