I am currently taking a class on post Civil War American history. So far, we have discussed Reconstruction and The Gilded Age, along with populism and socialism, among many other topics. The text that the professor has chosen is free and can be accessed as noted above. This is a great text with clear writing, many visuals and primary sources on all topics. It shows history as it was; this does not feel like a sanitized text. During our current historical period, you may want to look to and understand the past. If so, take a look at this textbook. I am learning a lot from it.
The American Yawp
A Free and Online, Collaboratively Built American History Textbook