Expiration Reminder VS DropTask

EssentialPIM - EssentialPIM is a free Personal Information Manager that keeps up with the times and lets you manage appointments, tasks, notes, contacts, password entries and email messages across multiple devices and cloud applications.

Task Coach - Task Coach is a simple open source todo manager to keep track of personal tasks and todo lists.

Todo.txt - Track your tasks and projects in a plain text file, todo.txt. A todo.

GTDNext - About Us.

Strikethru - Strikethru is a kind of to-do list notebook for managing work lists and staying updated with the important tasks.

CherryTree - A hierarchical note taking application, featuring rich text and syntax highlighting, storing data in a single xml or sqlite file.