This is a browser extension developed for Chrome (untested on Firefox, but should also work there) that adds a side panel when using the brat rapid annotation tool (https://brat.nlplab.org/) to more easily track annotations. This is useful for projects that have many entity types.
A working version is available here: https://chrome.google.com/webstore/detail/brat-extension/demacnmhgipjhklicbdfenbdfleekkej