Shells are an essential component of the operating system that act as an interface between the user and the kernel. They interpret user commands and execute them efficiently. While there are many shells available, not all of them are free and open-source. However, there are some excellent options out there that are not only free but also open-source, giving users the freedom to customize and enhance their shell experience.

In this article, we will highlight 19 of the best free and open-source shells that you can use on your operating system.

1. Bash (Bourne Again Shell): Bash is one of the most popular shells available and comes pre-installed on most Unix-based systems. It is highly versatile and has a wide range of features that make it suitable for both beginners and advanced users.

2. Zsh (Z Shell): Zsh is a powerful shell with extensive customization options. It includes advanced features such as autocorrection, spelling correction, and plugin support, making it a favorite among power users.

3. Fish (Friendly Interactive Shell): Fish is a user-friendly shell that is easy to use for beginners. It has a clean and modern interface with features like syntax highlighting and auto-suggestions.

4. PowerShell: PowerShell is a shell developed by Microsoft specifically for Windows users. It is a command-line interface that allows users to automate tasks and manage system configurations efficiently.

5. Tcsh (Tenex C Shell): Tcsh is an improved version of the C shell with additional features like command-line editing and history recall. It is a good choice for users who prefer a C-like syntax.

6. Ksh (Korn Shell): Ksh is an advanced shell that is compatible with both POSIX and Bourne shell scripts. It has powerful scripting capabilities and is commonly used in enterprise environments.

7. Dash: Dash is a lightweight shell that is designed for fast execution of scripts. It is the default shell on many Linux distributions and is well-suited for scripting tasks.

8. Elvish: Elvish is a modern shell that is built for interactive use. It has a powerful scripting language and features like auto-completion and syntax highlighting.

9. Tmux: Tmux is a terminal multiplexer that allows users to split their terminal into multiple panes. It is a great tool for managing multiple sessions and windows within a single terminal window.

10. Alacritty: Alacritty is a fast and lightweight terminal emulator that is designed for performance. It is highly customizable and supports features like GPU acceleration and custom keybindings.

11. Tilix: Tilix is a tiling terminal emulator that allows users to organize their terminal windows in a grid layout. It supports features like tabs, profiles, and custom layouts.

12. Kitty: Kitty is a fast and feature-rich terminal emulator that supports GPU rendering and Unicode fonts. It is highly customizable and has a clean and modern interface.

13. Xfce Terminal: Xfce Terminal is a lightweight terminal emulator that is part of the Xfce desktop environment. It supports tabs, profiles, and customizable keyboard shortcuts.

14. Terminator: Terminator is a terminal emulator that allows users to split their terminal window into multiple panes. It supports features like tabs, drag-and-drop reordering, and custom keybindings.

15. Guake: Guake is a drop-down terminal emulator that can be called up with a keyboard shortcut. It is highly customizable and supports features like tabbed windows and custom themes.

16. Roxterm: Roxterm is a lightweight terminal emulator that is designed for simplicity and ease of use. It supports features like tabs, profiles, and transparency.

17. Termite: Termite is a terminal emulator that is designed for minimalism and performance. It supports features like true transparency, custom keybindings, and full-screen mode.

18. Cool-Retro-Term: Cool-Retro-Term is a terminal emulator that emulates the look and feel of old-school CRT terminals. It supports features like customizable fonts, colors, and scanlines.

19. LXTerminal: LXTerminal is the default terminal emulator for the LXDE desktop environment. It is a lightweight and simple terminal emulator that supports basic features like tabs and profiles.

In conclusion, there are many excellent free and open-source shells available for users to choose from. Whether you are a beginner looking for a user-friendly shell or an advanced user in need of powerful scripting capabilities, there is a shell out there that will meet your needs. Experiment with different shells to find the one that best suits your workflow and preferences.