There are several productivity tools available that meet your requirements of being a one-time purchase and not requiring an account to use. Here are some options:
1. Everdo: This is a desktop app that allows you to manage your tasks, projects, and notes. It is available for a one-time purchase of $49.
2. TickTick: This is a task management app that offers a one-time purchase option. It is available for $27.99 for a lifetime license.
3. MyLifeOrganized: This is a task management app that is available for a one-time purchase of $59.95.
4. Nirvana: This is a task management app that offers a one-time purchase option. It is available for $149.99 for a lifetime license.
5. Task Coach: This is a free, open-source task management app that you...