What are the best tools for manually annotating textual topic segmentation?
Since I couldn't find a suitable tool, so I made a tool for textual topic segmentation. 

To anyone interested in this question, I forked YEDDA's entity recognition project and changed it, accordingly. You can check it here in GitHub: https://github.com/ThiagoSousa/YEEDASeg. My project is called YEDDASeg. 

Edit: People mentioned to use BRAT, but it is good to select a word and tag with with a label. My case is a bit more complicated, because it can be many paragraphs. In YEDDASeg, you basic just click on the text and press a key to label a topic in the text. It is simpler for this purpose.