here's how people in this thread manage their tasks:
by hand in notebook or on paper, in physical calendar
CalDAV (e.g. Nextcloud) tasks and compatible client software like Tasks dot org
CalDAV calendar: calendar events with reminders, e.g. Thunderbird
Software
Markdown notes like QOwnNotes, Obsidian, Trilium
Text based task software: Calcurse, TaskWarrior (BugWarrior, TimeWarrior, vit frontend)
Text editor based: Org mode, vimwiki, todo.txt
Task lists: Tasks dot org etc.
Kanban: Cryptpad’s kanban, jtxboard
Mindmaps like Freeplane