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 https://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 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 are used for tracking then:
they should be kept simple.
the number of individual spreadsheets should be kept to a minimum.
they must be updated regularly.
only one master copy should be maintained and everyone should know where the master copy is.
they should be accessible to all project members.
if security is an issue (often occurs at large companies) and common access is not possible, then copies may be distributed as long as everyone understands that these are copies and cannot be updated.
Again there are many proprietary tools for tracking bugs and feature requirements.