Issue Tracker
Originally, issue trackers were designed to help software developers log and resolve defect reports. Before long, teams started to use issue trackers to log all types of work. Today, products like Jira and YouTrack describe themselves as Agile Project Management tools that you can use to plan, track, and release great software.
From the perspective of building a continuous delivery toolset, a modern issue tracker can provide several key abilities in one package.
Project and issue tracking
Change management
Scrum and kanban support
Backlog prioritization and sprint planning
Agile reporting
Version control integration
Build tool integration
Static analysis integration
Many of today's hosting platforms, such as GitHub and Visual Studio Team Services, include issue tracking along with build management tools, and overlap with some of the core features provided by issue trackers.
The single most important thing you can do
If you use an issue tracker to log absolutely all the work being done to your code base, a truly amazing benefit is that you will have a well-known unique record for each work item.
Products like Jira and Visual Studio Team Services integrate with version control so that you can link commits to work items. Consequently, you can start with Git Blame and click through to the work item for a given commit, or start with the work item and drill down to the actual code-level changes made to implement the item.
I cannot overstate the usefulness of being able to audit changes against change requests, from either direction.
What you need to decide
There are several equivalent products available today. The crux of the decision can rest on what other tools you are already using or want to use.
If you are starting from scratch
For a open source project, you can use the free GitHub or Bitbucket tools until you outgrown them.
Better yet, apply for free support from Atlassian by completing the Open Source License Request.
For a closed source project, you can use Bitbucket and its tools for five users free.
For a larger project with five or more developers
If you are using a Jetbrains IDE, consider YouTrack.
If you are using Visual Studio, consider Visual Studio Team Services.
Otherwise, go with Jira. You won't regret it.
Except for GitHub, these suggestions are available in both cloud and on-premises versions.
The cloud platforms are both reliable and cost effective, though some plugins may only be available on premises.
Resource checklist
Related Topics
Tools Mentioned
Bitbucket (Atlassian)
Jira (Atlassian)
Visual Studio Team Services (Microsoft)
YouTrack (JetBrains)
See Also
Change management (ITSM) (Wikipedia)
18 Best Jira Alternatives for 2018 (WorkZone)