Apache, also known as Apache HTTP Server. It is the most widely used open-source web server software. It is developed and maintained by the Apache Software Foundation. It is a powerful and flexible server that allows hosting websites, serving web pages, and handling HTTP requests.

Key features of Apache include:

1. Cross-Platform Compatibility: Apache is compatible with various operating systems, including Linux, Windows, macOS, and Unix-like systems. This makes it highly versatile and widely adopted.

2. Performance and Scalability: It is designed to handle a large number of concurrent connections efficiently. It supports multi-processing modules (MPMs) that allow for different strategies in handling client requests, such as pre-fork, worker, and event models.

3. Configurability: It provides a rich set of configuration options, allowing administrators to customize its behavior to suit their specific requirements. Configuration files are written in a human-readable format, making it easier to modify and fine-tune the server settings.

4. Module Support: It offers a modular architecture, allowing the addition of various modules to extend its functionality. There are modules available for features like SSL/TLS encryption, URL rewriting, caching, proxying, authentication, and more.

5. Security: Apache incorporates various security features and supports encryption protocols like SSL and TLS. It provides options for securing the server, configuring access control, and implementing authentication mechanisms.

6. Virtual Hosting: It supports virtual hosting, which enables hosting multiple websites on a single server. This allows different domains or subdomains to be hosted independently, each with its own configurations and settings.

7. Logging and Monitoring: It provides comprehensive logging capabilities, allowing administrators to track and analyze server activity. Detailed logs can be generated, capturing information about requests, errors, and access statistics. Additionally, it can integrate with monitoring tools and generate performance metrics.

8. Community and Support: It has a large and active community of users and developers who contribute to its development, provide support, and share resources. The Apache Software Foundation offers extensive documentation, forums, mailing lists, and resources to assist users.

Apache's popularity and long-standing presence in the web server landscape make it a trusted choice for hosting websites and applications. Its flexibility, performance, and extensive features have made it the go-to web server for millions of websites worldwide.