I'm evaluating requirements tools for possible purchase, and Confluence is one I'm looking into.
Confluence is one I'm considering. Here are our needs. How does Confluence fit with them?
Identifier
Each requirement must have a unique identifier.
Single Database
Multiple (all?) requirements kept in a single database.
Relationships Between Requirements
Many-to-many relationships between requirements
Requirements Traceability Matrix
Able to generate an RTM, both top-down and bottom-up
Types of Requirements
Supports defining varying classes of requirement (i.e. Enterprise, System, Operational, Interface) with varying fields for each class (i.e. ID, Name, Description, Notes)
Reporting Capability
Workflow
There should be a capability to establish a workflow for generation and approval of requirements.
Baselining
There should be the capability to baseline requirements – for instance, tag a set of requirements as being for a specific release.
Rollback
There should be a capability to roll back requirements.
Yes, as @Davin Studer said, this is definitely a description of Jira. Most of your requirements can be fulfilled with Jira.