Graphical LaTeX writing tool for papers, books and formula-heavy documents.
LyX is open-source document processing software built on the LaTeX typesetting system but offering a graphical interface and a structured approach to writing. It suits theses, maths-heavy papers, books and technical reports.
Use cases: LaTeX writing, theses, formula documents, book typesetting, technical reports
Note: LyX lowers the barrier to LaTeX input, but you still need to understand document structure, templates and the compilation process.