To run one specific spec you can open it in editor and press Ctrl-Shift-F10 (on Windows) the same action available in context menu.
Also you can do this when the file is selected in Project View.
Note that if you edit spec file and press this shortcut it will run the spec in which caret is located (not all file)
Also RM allows run all specs/tests in particular directory. I'd suggest to check our help about this.
Hope this helps, Oleg.
auto-test functionality is available for specs too.
As for running single spec/example when something has been changed - IDE (or any other tool) can not do this since it doesn't know which specs/examples affected by the change.