I just made a research on web for the free operating systems which can be used as an alternative of Microsoft's Windows operating system. Here I'm listing some best operating systems that can be used with your personal computers and laptop, and many of them will give you much more sophisticated features that Microsoft Windows provides.
1. Ubuntu
Ubuntu is a community developed operating (Linux debian based)system that is perfect for laptops, desktops and servers. Whether you use it at home, at school or at work Ubuntu contains all the applications you’ll ever need, from word processing and email applications, to web server software and programming tools.
Ubuntu is and always will be free of charge. You do not pay any licensing fees. You can download, use and share Ubuntu with your friends, family, school or business for absolutely nothing.

2 . Mandriva
Mandriva Linux is a community-based Linux distribution, suitable for a wide range of situations from typical desktop use through development and server roles up to clustering.
Mandriva Linux is based on the Cooker development project sponsored by Mandriva. Hundreds of passionate free software developers work openly on the core of the distribution. This open, community-driven development system has been in place since 1998, making it one of the longest-standing open source development communities around. The involvement of the Mandriva development community helps us to make Mandriva Linux one of the largest, most up-to-date, integrated, internationalized and standardized distributions available.

3. Fedora Linux
Fedora is a Linux-based operating system that showcases the latest in free and open source software. Fedora is always free for anyone to use, modify, and distribute. It is built by people across the globe who work together as a community: the Fedora Project. The Fedora Project is open and anyone is welcome to join.
4. OpenSolaris
OpenSolaris is an operating system (OS), an open source project licensed under CDDL, and a community. The project’s goals are innovation, collaboration, and the extension of OpenSolaris technology.OpenSolaris is free, open source, and well-suited for desktops, laptops, servers, and data centers. The quality requirement of OpenSolaris is perhaps best stated as Production Ready All The Time.
5. Darwin
Darwin is the UNIX technology-based foundation of Mac OS X. Darwin integrates several technologies. Among the most important aredarwin screenshot 4.4BSD-based operating-system services (built on the Mach 3.0 microkernel), the I/O Kit, networking facilities, and support for multiple integrated file systems. Developers can use Darwin to port UNIX/Linux applications and create kernel extensions.
6. Kubuntu
Kubuntu is an operating system built by a worldwide team of expert developers. It contains all the applications you need: a web browser, an office suite, media apps, an instant messaging client and many more.Kubuntu is an open-source alternative to Windows and Office. Kubuntu is based on free software from many communities of developers including:
KDE Software, applications that give you power, Plasma, KDE's desktop and netbook workspaces,Linux, an operating system kernel taking over the world,Debian, supply most of our packages,Ubuntu, turning free software into distributions such as Kubuntu.
7.openSUSE
openSUSE is a free and Linux-based operating system for your PC, Laptop or Server. You can surf the web, manage your e-mails and photos, do office work, play videos or music and have a lot of fun!
1. Ubuntu
Ubuntu is a community developed operating (Linux debian based)system that is perfect for laptops, desktops and servers. Whether you use it at home, at school or at work Ubuntu contains all the applications you’ll ever need, from word processing and email applications, to web server software and programming tools.
Ubuntu is and always will be free of charge. You do not pay any licensing fees. You can download, use and share Ubuntu with your friends, family, school or business for absolutely nothing.

2 . Mandriva
Mandriva Linux is a community-based Linux distribution, suitable for a wide range of situations from typical desktop use through development and server roles up to clustering.
Mandriva Linux is based on the Cooker development project sponsored by Mandriva. Hundreds of passionate free software developers work openly on the core of the distribution. This open, community-driven development system has been in place since 1998, making it one of the longest-standing open source development communities around. The involvement of the Mandriva development community helps us to make Mandriva Linux one of the largest, most up-to-date, integrated, internationalized and standardized distributions available.

3. Fedora Linux
Fedora is a Linux-based operating system that showcases the latest in free and open source software. Fedora is always free for anyone to use, modify, and distribute. It is built by people across the globe who work together as a community: the Fedora Project. The Fedora Project is open and anyone is welcome to join.
4. OpenSolaris
OpenSolaris is an operating system (OS), an open source project licensed under CDDL, and a community. The project’s goals are innovation, collaboration, and the extension of OpenSolaris technology.OpenSolaris is free, open source, and well-suited for desktops, laptops, servers, and data centers. The quality requirement of OpenSolaris is perhaps best stated as Production Ready All The Time.
5. Darwin
Darwin is the UNIX technology-based foundation of Mac OS X. Darwin integrates several technologies. Among the most important aredarwin screenshot 4.4BSD-based operating-system services (built on the Mach 3.0 microkernel), the I/O Kit, networking facilities, and support for multiple integrated file systems. Developers can use Darwin to port UNIX/Linux applications and create kernel extensions.
6. Kubuntu
Kubuntu is an operating system built by a worldwide team of expert developers. It contains all the applications you need: a web browser, an office suite, media apps, an instant messaging client and many more.Kubuntu is an open-source alternative to Windows and Office. Kubuntu is based on free software from many communities of developers including:
KDE Software, applications that give you power, Plasma, KDE's desktop and netbook workspaces,Linux, an operating system kernel taking over the world,Debian, supply most of our packages,Ubuntu, turning free software into distributions such as Kubuntu.
7.openSUSE
openSUSE is a free and Linux-based operating system for your PC, Laptop or Server. You can surf the web, manage your e-mails and photos, do office work, play videos or music and have a lot of fun!