Subtasks Navigation App allows you to effectively navigate within all the subtasks of a common parent directly from the detail view. Additionally, the progress bar shows how far are you from the parent issue resolution. The currently displayed subtask is highlighted. All the subtask's actions are available including bulk operations.
The application adds new section called "Other subtasks" to detail view of a subtask. This section contains a list of all "siblings" of the subtask (including the subtask itself, which is highlighted).
Here is the description of its most important components (please see the image below):
A: Progress bar informing about subtasks
B: Context menu, where you can perform a Bulk operation or Open issue navigator.
C: Click on this arrow (or alternatively anywhere on the particular subtask row) to quickly display description of a sibling subtask.
D: Add a new subtask to the parent issue.
The agile view contains "Other subtask" view section as well (see the image below). This "Other subtask" view is a bit simplified compared to the subtask detail view.
Subtask Navigation app will be displayed only on issues of projects which were enabled in the admin section. In other words, you can show or hide the app per project as shown on the image below.