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.selenium.dev/.
JMeter is used to track requests and can be used for functional, performance, and stress tests.
For more information, see https://jmeter.apache.org/.
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 which 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 spreadsheets are used for tracking, then:
Again there are many proprietary tools for tracking bugs and feature requirements.