A common tool in the open source community is the brat annotation tool. It's free and offers entity and relationship labeling.
I actually started a company Datasaur and we also offer our online labeling tool for free to academics, which includes entity labeling, relationship labeling, integration with popular libraries such as spaCy/NLTK and workforce management capabilities. If you're interested in trying this out, shoot an email to academia@datasaur.ai and we'll get you set up!
