Portland-based Monsoon, a developer of software for creating online marketplaces, has been acquired by online bookseller Alibris. According to Alibris, it is acquiring Monsoon with funding from Oak Hill Capital, the private equity backer of the firm, along with bank funding from Square 1 Bank. Alibris said it will continue to operate the two firms as separate businesses. Financial details of the cash-and-stock deal were not disclosed.