Not a tool, but still very convient, so it's probably useful to promote it here: The input language HDDL (Hierarchical Domain Description Language) can be used to describe HTN planning problems, and there are two repositories available with a rangle of domains described in HDDL (see below). The website for the IPC 2020 also features test instances and more as the domains used were provided in HDDL.
LaTeX listings syntax highlighting for HDDL, JSHOP's input language, and PDDL. Created by Mauricio Cecilio Magnaguagno. Find it on git
Tool for drawing HTN solutions given the required output format of the IPC 2020. Also kindly provided by Mauricio Cecilio Magnaguagno.
Git Repository with the IPC 2020 benchmarks described in HDDL.
Another git Repository for additional HTN domains described in HDDL. Please contact Gregor Behnke and Pascal Bercher if you'd like to add your domain here as well.
Note that the IPC 2020 website website also features various minor "test case benchmarks" as well as a translator into various other input formats.