Zotero - Zotero is a free, easy-to-use tool to help you collect, organize, cite, and share research.
Annotable - Ultimate image annotation & markup tool
Qiqqa - Qiqqa is a free research and reference management software. It can be used in many organizational projects from the academic to the personal to the business endeavor. Read more about Qiqqa.
Hover Me - Hover me lets you quickly annotate any image and easily integrate an interactive version within your own website.
JabRef - Graphical Java application for managing bibtex (. bib) databases.JabRef · JabRef Help · JabRef | Blog · OpenOffice/LibreOffice .
Picsell.ia - Annotate datasets smarter, 10x faster & cheaper.