Papers is a powerful tool I use regularly from my web browser to catalog and annotate published papers (and other files) easily. The lists (essentially, a virtual directory structure) feature makes it easy to organize papers by subject, project, etc... and they can exist in multiple lists without requiring any duplication of files. The feature set is probably a lot more robust than I make use of, but for managing sources and quickly accessing and building references lists, it's an easy to use solution.

What I like the most about papers by ReadCube is how easy it makes to import papers from databases to my own library. A single click and the paper is in the library, with all the data extracted and easy to find, making it very easy to manage the library.

I love being able to read, annotate, and group my research papers together in an easy way. ReadCube makes it very convient to organize all of the research papers I read and cite in my own research, making citations a much easier process.