Eric Gentry writes:
Mesh Align Plus is a precision modeling addon (free/open source) that lets you move mesh parts and objects around, by picking points of interest and using them as targets for alignments, rotations and other types of transformations. For example: rest a plane against the tips of three separate pyramid objects...or select an edge and rotate part of your mesh around it (or even take that axis and shift it to a new location, then rotate from there).
There are Quick Tools for fast and easy access to common operations (like aligning real points, lines or planes together), and Advanced Tools (for working with imaginary/implied geometry, measuring and calculating quantities in your scene, like line length or face normals, and composing new targets for your transformations).
Come test it out, and help develop the next/improved version of the tool! :)
See the youtube demo video below (or read the wiki/manual) for more information, and to get a complete view of the addon's capabilities.