A preprint is a draft version of a research paper that has not yet been subject to a review. It may have already been submitted to a publisher at the same time but not yet formally peer-reviewed, but this does not have to be the case. Even though a preprint can in theory be disseminated via any medium, in practice they are often archived and disseminated on central repositories. The community members of these repositories then receive a message and can check uploaded content. There are several of these kinds of repositories or preprint servers.
Cross-disciplinary repositories in which you are able to search for preprints are:
You can find further repositories using the search services for repositories.
You can find further repositories with the overview lists of repositories.