- Searching all issues for an organization

- Voting on issues (not just :+1:)

- Public issues for private repos

- Attaching files (repros, necessary files, etc.)

- Dependencies/links

- Priority (you can label priority but not sort by it)

- Metrics of any kind

https://www.zenhub.io/

It adds these features to improve the GitHub Issue tracker directly into GitHub.com, allowing you to:

- Display issues on a task board by priority and progress - Attach any file type to an issue - Add estimates and view burndown charts / metrics attached to them - +1 issues to avoid excess comments - Improved search functionality - Link repos together to view issues that span multiple projects

Without having to context switch out to a separate issue tracker or UI

----

Disclosure - I work at ZenHub, and use it with GitHub all day :D