Swimlanes.io

Swimlanes.io is a browser-based tool for creating and sharing sequence diagrams. Its clean UI, text-driven diagram definition language and the fact that its full feature set is available for free makes this our default choice for working with sequence diagrams.

As compared to WebSequenceDiagrams, swimlanes is cleaner, with a more modern look and feel, and has a richer feature set, including exports of higher resolution images and PDFs.