bookit is a Chrome add-on developed by serenenight that allows users to easily check the availability of books in university libraries while browsing book pages on platforms like Douban and Amazon. This free tool is specifically designed for users in China and currently supports a number of universities in Beijing, Shanghai, Jiangsu, Shaanxi, Sichuan, Hubei, Anhui, Zhejiang, Shandong, Heilongjiang, Jilin, Fujian, Hebei, Guangdong, Liaoning, Jiangxi, Inner Mongolia, Yunnan, Ningxia, Gansu, Taiwan, and Hong Kong.

With bookit, users can instantly see whether a book is available in their university library without having to visit the library's website. The add-on conveniently displays the corresponding university library's collection on the book page, making it easy for users to make informed decisions about purchasing or borrowing books.

Please note that bookit does not currently support all universities in China. However, the developer encourages users from unsupported universities to contact them for further assistance.

Overall, bookit is a useful and time-saving tool for students and researchers who frequently check library collections while browsing for books online.