The traditional aeolian harp is essentially a wooden box including a sounding board, with strings stretched lengthwise across two bridges. It is placed in a slightly opened window where the wind can blow across the strings to produce sounds. The strings can be made of different materials (or thicknesses) and all be tuned to the same note, or identical strings can be tuned to different notes.
And here is a clip, by Sarah Deere "Jones Celtic and Aeolian Harp"