It is interesting to observe how mainstream PIM applications get features explored a decade ago by research community. Email threads for example were explored back in 1993 in email client Mona . This time it's tasks again:
We know (from my paper) that email has been always extensively used for other activities besides its primal role - communication [2, 3]. People manage tasks, delegate work, backup files, send themselves reminders and use email for several other activities which were not envisioned by email creators. This flexibility of email has its drawbacks as well, as important emails can easily be buried in inbox with less important ones. The diversity of usage has led to several prototypes.
Research PIM prototypes
Raton Laveur (2000) integrated calendar, to-do list and notes in a regular inbox to provide support for tasks reminders . To reduce clutter (of mixed information in the inbox) and cognitive effort (to file information), it allowed grouping and searching for information with users’ defined and predefined queries (unseen, completed to-dos, etc.). TaskMaster (2003) also had task management incorporated in the email client where each task (called thrask by authors as a combination of words thread and task) could include a list of emails, URL’s and attached files . All this information could be viewed in an internal viewer without leaving the email client. Each thrask could have associated clusters of actions and a due date (additional attributes). The due dates were presented with graphical elements which were always visible and changed accordingly to approaching due dates. The tool was positively accepted by participants but was never developed in a fully functional email client. One of the drawback of both tools is added complexity and cognitive load with several organizing mechanisms.
An interesting approach was used in TimeStore (1997) - a time-based email visualization . This email client visualized emails as dots on a two dimensional grid with time on horizontal axis and contacts on vertical axis. In this view a user could see rhythms of conversations (on which days a particular person sent emails or emails were sent to), but the subject of each email was obscured. Users could create additional notes on each email to support tasks. This time-based visualization provided a reminding function with visually emphasised emails (tasks) that moved too far away in the past and a list of contacts that helped as social reminders. TimeStore vision was to completely abandon the traditional inbox view and free users from filing. The tool inspired another grid based email prototype called TaskView (2002). This prototype provided a matrix view of email messages with dates on the top axis and email subjects on a side (day/subject as opposed to day/sender in TimeStore) . While both prototypes provide a better overview of tasks in emails, they also lacked the regular inbox view in which users can search for their emails by subjects, dates, senders and other standard email attributes.
Some present email clients have tasks management embedded in email interface. Outlook version 2007 has a task list, to which emails can be dragged to as new tasks. Gmail has an extension called Taskforce which splits emails in three categories: information, action and broadcast. Tasks can be created from its interface or from email, can be shared and can have files attached as well. Thunderbird also has several extensions that provide reminding capabilities of to-do’s and tasks integrated in a calendar. But there is still room for improvement of design of these tools, integration (e.g. calendar with tasks in Outlook) and reminding functionalities.
 A. Cockburn and H. Thimbleby. Reducing user effort in collaboration support. In IUI ’93: Proceedings of the 1st international conference on Intelligent user interfaces, pages 215–218, New York, NY, USA, 1993. ACM.
 W. E. Mackay. Diversity in the use of electronic mail: a preliminary inquiry. ACM Transactions on Information Systems (TOIS), 6(4):380–397, 1988.
 N. Ducheneaut and V. Bellotti. E-mail as habitat: an exploration of embedded personal information management. Interactions Magazine, 8(5):30–38, 2001.
 V. Bellotti and I. Smith. Informing the design of an information management system with iterative fieldwork. In DIS ’00: Proceedings of the 3rd conference on Designing interactive systems, pages 227–237, New York, NY, USA, 2000. ACM.
 V. Bellotti, N. Ducheneaut, M. Howard, and I. Smith. Taking email to task: the design and evaluation of a task management centered email tool. In CHI ’03: Proceedings of the SIGCHI conference on Human factors in computing systems, pages 345–352, New York, NY, USA, 2003. ACM.
 K. S. Yiu, R. Baecker, N. Silver, and B. Long. A time-based interface for electronic mail and task man- agement. Advances in human factors/ergonomics, pages 19–22, 1997.
 J. Gwizdka. Taskview: design and evaluation of a task-based email interface. In CASCON ’02: Proceed- ings of the 2002 conference of the Centre for Advanced Studies on Collaborative research, page 4. IBM Press, 2002.