A few things you can do that don’t involve any new software. The first two do (almost) what you want. The other two may be useful, for similar tasks but are not the same.
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Use the dock. If you click on an app’s icon in the Dock, all of its windows will be brought to the top. One side effect (which may or may not be a big deal for you) is that if the app doesn’t have any windows open, this will usually cause it to open a new window or create a new document.
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Use the CMD-TAB shortcut. When you select an app with CMD-TAB, all of its windows are brought to the top.
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Use Mission Control. Activate it with one of the system gestures (swipe-up with four fingers, use the Mission Control key on Apple keyboards or a keyboard shortcut you configured). You will see all the windows on your desktop, grouped by application. Clicking on one will bring that window to the top (but won’t bring the rest of the app’s windows with it).
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Use App Exposé (aka Application Windows). Activate it with one of the system gestures (swipe-down with four fingers, press the Mission Control key while holding CTRL or a keyboard shortcut you configured). You will see all of the windows belonging to the current app. Select one to bring it to the top.