I think Blizzard got this right in StarCraft and WarCraft III. During a game, there is a 3x3 (or 3x5) grid on the bottom right that sort of looks like a numpad. When you have units selected, the grid will show the actions, and only those actions, that correspond to those units.

Technically, you never see "all" actions - you only see the actions that make sense for the selected units. However, because there is a predictable place where the actions will show up, and because you know those are all the actions that are there, it never feels confusing.

On the contrary, it lets you quickly learn what the different skills are for each unit.

There is also a "default" action that will happen when you right-click somewhere on the map. What this default action will do is highly context specific and irregular: e.g. right-clicking on an enemy unit will trigger an attack order, but only if your selected unit actually has a matching weapon, otherwise it will trigger a move order. Right-clicking a resource item will issue a "mine" order, but only if you have selected a worker, etc etc.

Instead of trying to teach you all those rules, or to let you guess what the action is doing, the UI has two simple rules:

- How the default action is chosen may be complicated, but it will always be one of the actions from the grid.

- If a unit is following an action, that action will be highlighted in the grid.

This means the grid doubles as a status display to show you not just what the unit could do but also what it is currently doing. It also lets you learn the specifics of the default action by yourself, because if you right-click somewhere, the grid will highlight the action that was issued.

The irony is that in the actual game, you almost always use the default action and very rarely actually click the buttons in the grid. But I think the grid is still essential for those reasons: As a status display and to let you give an order explicitly if the default isn't doing what you want it to do.

The counterexample would be the C&C games: The UI there only has the right-click mechanic, without any buttons, with CTRL and ALT as modifier keys if you want to give different orders. But you're much more on your own to memorize what combination of CTRL, ALT, selected unit, target unit and click will issue which order.