Through Joannie Think, a useful taxonomy of experimental task (for psychologists and CSCW researchers). It's actually taken from McGrath, J.E., "Groups: Interaction and Performance", Prentice-Hall, Inc, Englewood Cliffs, N.J., 1984.

1. Planning Tasks: Generating plans; Key notion: Action-oriented plan 2. Creativity Tasks: Generating ideas; Key notion: Creativity 3. Intellective Tasks: Solving problems with a correct answer; Key notion: Correct Answer 4. Decision-making Tasks: Dealing with tasks for which the preferred or agreed upon answer is the correct one; Key notion: Preferred answer 5. Cognitive Conflict Tasks: Resolving conflicts of viewpoint; Key notion: Resolving policy conflicts 6. Mixed-Motive Tasks: Resolving conflicts of motive-interest; Key notion: Resolving pay-off conflicts 7. Contests/Battles: Resolving conflicts of power; competing for victory; Key notion: Winning 8. Performances: Psychomotor tasks performed against objective standards; Key notion: Excelling