Additional Study Information: In this research study, an investigational medication named ACR-368 (also known as prexasertib) is being tested for the treatment of ovarian carcinoma, endometrial adenocarcinoma, and urothelial carcinoma. In this study, ACR-368 is being tested when it is given alone (called monotherapy) and when it is combined with low doses of a chemotherapy medication named gemcitabine (called combination therapy). ACR-368 has not been approved for use as a treatment for any condition, by government agencies in any country. ACR-368 is a type of medication called a checkpoint kinase inhibitor which may prevent cancer cells from repairing itself themselves, resulting in the death of cancer cells. Gemcitabine is a medication that treats cancer by destroying fast-growing cells in the body (called chemotherapy). In this study, gemcitabine is not used to destroy cancer cells, but it is used at low doses to increase the effectives of ACR-368. Gemcitabine is approved in the United States (U.S.) by the U.S. Food and Drug Administration (FDA) for the treatment of certain cancers, but it has not been approved at the specific doses in the specific types of cancers that are part of this study. In this study, since low doses of gemcitabine are used, it is not expected to kill cancer cells but is being studied to see if it helps ACR-368 kill tumor cells. The combination of ACR-368 and low-dose gemcitabine has not been approved and is considered investigational.