Engineering design (piping and mechanical equipment) and precise sketching to convey ideas to clients, sometimes including structural, architecture and electrical in supplement to mechanical.
Technical illustrations for a technical book that I wrote in the last company where I worked before retiring.
Home projects in my former house.
Home projects illustrations for relatives.
Fabrication drawings and templates for acrobatic kites (2 lines and 4 lines) as well as single line kites. These are personal kites, not for a business.