Is there any way to show all GitHub tickets without an assignee?

@LyndenShields's answer doesn't seem to work anymore.

At this date (March 16, 2015), the way to search for issues that have no assignee is to use the no: qualifier in the issues Filter field:

no:assignee

Alternatively, you could use the following query string to achieve the same:

https://github.com/<username>/<repo>/issues?q=no%3Aassignee

EDIT: Note that I could not make it work if I only had one qualifier specified (ie. you may need to add another one and have it like no:assignee is:open).

EDIT #2 (March 16, 2016): the above edit is not accurate anymore (hence the strikethrough); GitHub now accepts search queries with one qualifier only.

EDIT #3 (July 26, 2017): removed the %01 from the end of the URL - it basically is an unused character, but I believe GitHub interpreted it as a space. Indeed, when you use it this way, GitHub will automatically add a space, I guess to make sure other qualifiers can easily be added. Strangely, though, it will add a %20 to the end of the URL today, but again, you can simply omit that part. The %3A between the words no and assignee is the character code for Colon. See a full list here.

EDIT #4 (June 30, 2020): this is now possible via the UI: simply go to your issues list (https://github.com/<username>/<repo>/issues) then choose Assigned to nobody from the Assignee dropdown:

Go to the issues list and show issues assigned to yourself. Look in the URL bar and change where it has your username to none just after 'assigned/' and press enter. The UI will look the same but the list will have only unassigned issues.

e.g.:

https://github.com/<username>/<repo>/issues/assigned/none

One workaround would be to compare:

• the list of issues
• with the list of issue assigned to anyone

(the difference being the list of issues not yet assigned)

See GitHub V3 Api "list-issues-for-a-repository" section:

assignee

String User login

• none: for Issues with no assigned User.
• *: for Issues with any assigned User.