Daisy is a free open-source widget for Plasma/KDE.

Main features:
- Three types of roles: circular dock, media controller and linear dock
- Can dock in any screen position and be used in Horizontal or Vertical 
  mode (linear dock role)
- Configuration tools to access all configurable options
- Launchers can be edited with a simple right-click
- Hybrid launchers to launch applications and control running tasks
- Plugins to provide information and execute several tasks
- Various backgrounds available
