Here's a list of concepts, philosophies, and methodologies I use from time to time.

• GTD - a personal framework for self-organization
• Kanban - a way for individuals or groups to organize information flow
• Holacracy - a way to structure flat, collaborative organizations
• Stickies - concise, flexible canvas to write, share, and interact with
• Whiteboard - a decent drawing surface
• Process Mapping / Journey Mapping / Workflow Diagramming - tools that model higher-level thinking that influences product and/or service design