References in order of first mention

Daytimer -

https://www.daytimer.com/

PalmPilot -

https://en.wikipedia.org/wiki/PalmPilot

Gina Trapani -

https://en.wikipedia.org/wiki/Gina_Trapani

Todo landing page -

http://todotxt.org/

Todo file format -

https://github.com/todotxt/todo.txt

Dropbox -

https://www.dropbox.com/

Simpletask -

https://github.com/mpcjanssen/simpletask-android/

QTodoTxt -

https://github.com/QTodoTxt/QTodoTxt

Synology DS220J NAS -

https://global.download.synology.com/download/Document/Hardware/DataSheet/DiskStation/20-year/DS220j/enu/Synology_DS220j_Data_Sheet_enu.pdf

Ice_recur -

https://github.com/rlpowell/todo-text-stuff

Py_recur -

https://github.com/TASpinner/py_recur

Microsoft todo -

https://to-do.office.com/tasks/