Legacy Uke
Workshop

Software

Tablature

Guitar Pro 8
GuitarPro - Home Page
This is the only application here that is purchased - and it's worth it. After going through multiple freeware applications and trials of a few paid applications I found that GuitarPro was the best for me. Feature rich, very customizable, and excellent support make this a winner. If you are going to write tablature or even just want to have a tool that does all the musical syntax checking, transpose, and lots of other features then GP is worth the money.
MuseScore - Home Page
One of the better freeware applications for tabs. MS also has support for integration with LibreOffice if you are inserting musical symbols or pieces of music into LibreOffice documents.

Audio

Audacity - Home Page
Soundtrack editing software. Many functions including those useful if you tabbing music, pitch change without changing tempo.
THR Editor - Download Page
THR Editor is the software component of the Yamaha amp. For the ukulele I found that the THR5 amp was more than enough for volume and creating custom tones.

Documentation/Images

LibreOffice - Home Page
LibreOffice (formerly OpenOffice) is the open-source, free office productivity suite. The suite can function as a complete replacement for Microsoft Office applications. For web development I use Draw for creating strawman layouts and basic graphics/text. By designing in Draw the graphics can be copied into GIMP and saved as individual images. (All LibreOffice documents can be exported as PDF.)
PDF-XChange Editor - Home Page
PDF-XChange is available both in free and "Pro" (paid) versions. I used this software for annotating PDF files and creating watermark effects on Windows. This is a handy tool for editing a PDF outside the limitations of standard PDF editors. [Note: There is not a Linux version of this application so a different one is used on the Ubuntu Studio.]
Xournal++ - Home Page
Xournal is advertised as a note taking application with the capability to modify/annotate numerous types of documents. This application is cross-platform making it a great tool for anyone. I have found it best to do as much markup as possible in GuitarPro before adding additional comments and images.
Gimp - Home Page
The GNU Image Manipulation Program (GIMP). GIMP is a cross-platform image editor available for GNU/Linux, macOS, Windows and more operating systems. GIMP is the free equivalent of Adobe Photoshop.
Inkscape - Home Page
Vector drawing is a way to create graphics that can change size without impacting resolution. Once a logo or text has been created it can be resized without impacting the quality.

3D Printing

Inkscape - Inkscape
Vector graphics (SVG format) can be used in 3D design. Tinkercad is my preferred CAD application because its free - and easy to use. Uploading vector images expands the functionality of TinkerCAD.
TinkerCAD - Home Page
TinkerCAD is a cloud-based design tool for electronics, coding, and 3D design. The application is easy to used with a broad support base. If you aren't designing really complex CAD projects, TinkerCAD is a free solution that works well for most of my applications. Combined with another tool like Inkscape or modifying an existing model makes this a very capable app.
Thingiverse - Home Page
Technically not a tool - this is a source of free 3D models. Thingiverse is my favorite place to go browse and provided the base model that I built on my desk clamps with.

Other

Ubuntu Studio
Ubuntu Studio is a complete Linux operating system for those working with multi-media.