The following are two Open Source Testing tools:
Selenium is used for function testing in a browser with one user per activity. It records testing steps (clicks) as either HTML tables or Java classes.
For more information see https://www.seleniumhq.org/.
JMeter is used to track requests and can be used for functional, performance and stress tests.
For more information see http://jakarta.apache.org/jmeter/.
There are also many proprietary tools for automating tests and managing test plans.
The following tools are easily available. However a key issue in all cases is the availability of the data to all members of the project team - partner and customer.
A bug-tracking system that can be configured to your own requirements.
Although not specifically a bug-tracking tool, spreadsheets are often misused for this purpose as they are easy to understand and most users have experience of their functionality.
If these are used for tracking then:
Again there are many proprietary tools for tracking bugs and feature requirements.