doo
Todoist
Mendeley
BibDesk
EndNote
Zotero
Reminder
JabRef
Qiqqa
Mendeley
Zotero
JabRef
Citavi
Docear
Paperpile
BibDesk
Qiqqa is by far the strongest solution for research and managing pdf's. Zotero, named as a comparison is weak as it does not allow pdf;s to be loaded into its interface - you need to use a pdf reader, which defeats its whole purpose. With Qiqqa documents in a library can be searched together. It has excellent maps of your libraries. It is not prefect, having a few glitches, but still is the only one of its kind.
Todoist - Todoist is a to-do list that helps you get organized, at work and in life.
Mendeley - Easily organize your papers, read & annotate your PDFs, collaborate in private or open groups, and securely access your research from everywhere.
Zotero - Zotero is a free, easy-to-use tool to help you collect, organize, cite, and share research.
BibDesk - BibDesk is an organizational software created to help you edit and manage your bibliography. It keeps track of your bibliographic information as well as said information's associated web links and files. Read more about BibDesk.
JabRef - Graphical Java application for managing bibtex (. bib) databases.JabRef · JabRef Help · JabRef | Blog · OpenOffice/LibreOffice .
EndNote - Accelerate Your Research. Save time, stay organized, collaborate with colleagues and get published with EndNote 20.
