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Examples are git and mercurial (core systemsystems) and gihub , github (cloud provider), gitlab (software and cloud provider and software), ), Stash/Bitbucket from Atlassian (software and cloud provider), ...
Issue tracking
Issues are a way of managing development tasks based on requirements spanning from feature requests to bug reports. Issues can be entered by both developers, e.g. as a feature from a queue for to develop in a sprint, or usesusers, e.g. as feature requests or bug reports. Issues typically go through phases and may are assigned to people. Branches and commits often refer to issues.
Systems for issue tracking may be both integrated and standalone. Examples are github and gitlab (integrated), Jira from Atlasssian (standalone, but integrated with other Atlassian products), bugzilla (standalone), ...
Continuous integration (CI)
CI is a general term for building, testing and deploying the system you are developing, mainly to ensure it's quality, but also to automatically roll out new versions. CI is often automated by tools like ant, maven and gradle. These tools can be run locally, and/or on specialised servers that run build jobs on server farms. The advantage is both making builds independent of the individual developers and scaling to large systems. The build jobs may be triggered manually or automatically, when new code is committed and pushed to a code repository.