Offenbach is located directly on the eastern city border of Frankfurt am Main (you would call it one city). However, people from both cities have strong prejudices against each other's city. In the 1970s politicans tried to bring together both cities with no success.
Like Frankfurt it's a very international city. More than a third of the residents have no german passport (this rate is at an average of 8% nationwide). Offenbach on the river Main is also famous for its manufacturing of leather goods and clothing.
Living in Offenbach means living close to nature. This contributes to the high quality of life here. The city is surrounded by woods and public forests on three sides. On the fourth the river Main flows along the old city center and its beautiful promenade.