CiteULike is a free service to help academics to share, store, and organise the academic papers they are reading. When you see a paper on the web that interests you, you can click one button and have it added to your personal library. CiteULike automatically extracts the citation details, so there's no need to type them in yourself. It all works from within your web browser. There's no need to install any special software.
Because your library is stored on the server, you can access it from any computer. You can share your library with others, and find out who is reading the same papers as you. In turn, this can help you discover literature which is relevant to your field but you may not have known about.