Unwrap Me - Auto UV Seams is an automatic seam generator built exclusively for Blender by Shift A Technologies, based on computer graphics research. Instead of placing seams by hand, you can seam an entire mesh at once or grow UV islands by selecting one or more faces, watching charts spread across the mesh around those selections.
An Auto Seam operator built on a fast algorithm handles meshes up to millions of faces, and an Edge Walk operator creates seams along edge loops. The Developability setting limits stretch-error so the final unwrap carries less distortion, and Unwrap Me can remove self-intersecting chart overlaps caused by Blender's unwrapper. It generates seams on complex meshes with bad topology and produces larger, better connected, similarly sized charts than UV Smart Project.
Charts won't grow past existing seams or hidden faces, so you can seam some parts manually and let the addon handle the rest. Unwrap Me is open-source and still experimental, with free updates. It runs on Windows and Linux, and macOS is not currently supported.