Name the on-click menu-in-circle-around-object interface

What is the name for this type of interface?

I would like to learn more about it but first I need to find it's proper name. Any links to related reading are welcome.

EDIT: While adding tags I have discovered the radial-menu tag that led me to a Pie menu on Wikipedia. Links to related reading are welcome. How usable or recommended is the radial menu?

Answer

The biggest advantage of radial or pie menus is their speed. To quote this article.

Radial Menus Are Fast

Radial menus are faster to access than list-based menus in every kind of pointer-based UI, including cursor, stylus, and touch. One big part of that is because every option is spaced at the same distance from the pointer. That’s classic Fitts’ Law: the closer the target and the bigger it is, the easier and faster it is to hit.

Even better: you get faster with radial menus over time, because they take advantage of muscle memory in a way that list-based menus cannot. Radial menus are essentially gesture-based: touch-swipe-release. That’s why some call radial menus “marker menus”: it’s like making a mark on the screen. Swiping to 2 o’clock has one meaning, and swiping to 6 o’clock another. Like all physical actions—playing an instrument, typing a keyboard, serving a tennis ball—gestures get embedded in muscle memory, which is faster to access than visual memory. Tap-swipe is faster than scanning for an item in a linear list, just like touch-typing is faster than hunt-and-peck.

The same article references two rather old research papers which have this to say on the merits of radial selections

Research paper 1 : Do note this paper is no longer available on the net hence there is no way to validate if the reference is correct.To quote the article

The research on this has been in the can for nearly 25 years. A 1988 study did the comparison and found that for a specific test of eight-item lists, users were faster with radial menus than linear ones. And it turns out that speed only improves.

Research paper (2) - User Learning and Performance with Marking Menus : This is the article linked in the earlier extract and the summary is given below

The more you use radial menus, the faster you become. That was borne out in a 1994 study by Bill Buxton and Gordon Kurtenbach, who tested radial-menu speed with a stylus. Over time, they found that expert users stopped looking at the menu at all. They no longer needed the visual cues and went entirely “blind,” marking the screen with gestures, or “marks,” instead of pecking at buttons:

Using a mark on average was 3.5 times faster than selection using the menu. … A user begins by using the menu, but, with practice, graduates to making marks. Users reported that marking was relatively error free and empirical data showed marking was substantially faster than using the menu. … Marking menus, however, are not appropiate when the list of items changes dynamically. In this situation, users can still use the menus but will never graduate to using marks since menu item locations change.

There have also been multiple usability tests conducted on the usability of radial menus as quoted in this article

Jack Callahan's study compares the seek time and error rates in pies versus linear menus. There is a hypothesis known as Fitt's law, which states that the "seek time" required to point the cursor at the target depends on the target's area and distance. The wedge-shaped slices of a pie menu are all large and close to the cursor, so Fitt's law predicts good times for pie menus. In comparison, the rectangular target areas of a traditional linear menu are small, and each is placed at a different distance from the starting location.

Callahan's controlled experiment supports the result predicted by Fitt's law. Three types of eight-item menu task groupings were used: Pie tasks (North, NE, East, and so on), linear tasks (First, Second, Third, and so on), and unclassified tasks (Center, Bold, Italic, and so on). Subjects with little or no mouse experience were presented menus in both linear and pie formats, and told to make a certain selection from each. Those subjects uising pie menus were able to make selection significantly faster and with fewer errors for all three task groupings.

The fewer the items, the faster and more reliable pie menus are, because of their bigger slices. But other factors contribute to their efficiency. Pies with an even number of items are symmetric, so the directional angles are convenient to remember and articulate. Certain numbers of items work well with various metaphors, such as a clock, an on/off switch, or a compass. Eight-item pies are optimal for many tasks: They're symmetric, evenly divisible along vertical, horizontal, and diagonal axes, and have distinct, well-known directions.

Gordon Kurtenbach carried out an experiment comparing pie menus with different visual feedback styles, numbers of slices, and input devices. One interesting result was that menus with an even number of items were generally better than those with odd numbers. Also, menus with eight items were especially fast and easy to learn, because of their primary and secondary compass directions. Another result of Kurtenbach's experiment was that, with regard to speed and accuracy, pens were better than mice, and mice were better than trackballs.