Hardinfo is free software that allows to obtain information on the material that makes up your computer.
Motherboard model, cpu, RAM size, operating system … everything is there.
The utility also offers the ability to generate reports in HTML format (useful to get help on a forum) or to benchmark their machine.
To install Hardinfo, open a terminal as root and run the following command for rpm-based distribution:
yum install hardinfo
And this one for debian based distro:
sudo apt-get install hardinfo
You can then launch the program with the command hardinfo.