What is the Tech Radar?

My version of Tech Radar is a list of technologies, complemented by an assessment result, called ring assignment. I use four rings with the following semantics:

• USING — Technologies that I worked in the past and I love to work with. Either my day to day job or my hobby projects are related with them.
• LEARN — Technologies that I want to try and reading about currently. Eventually, they will end-up in USING section.
• INTEREST — Technologies that are promising and have clear potential value-add for me; technologies worth to invest some research and prototyping efforts in to see if it has impact.
• HOLD — Technologies not recommended to be used for new projects. Technologies that I think are not (yet) worth to (further) invest in. HOLD technologies should not be used for new projects, but usually can be continued for existing projects.