The Software is free.
A few important features in the long list include:
stability - it's continuously supported by the open source community, reducing the bugs and errors.
portability - Apache is available for multiple OS
Customizability - custom modules can be built easily.
Efficient handling of client requests.
Most popular webserver on the internet.
Room for Improvement:
No support is available from Apache software foundation.
Apache needs fine tuning of its components when in a larger environment, otherwise it can make your server unresponsive.
The webserver survey showed by netcraft [netcraft.com] says, "Apache is still the most widely used [61%] webserver in the world of internet." Apache is designed in such a way that different components of the system can be connected together easily. The beauty is that you can replace or add a component or feature without affecting the system. Apache is a powerful tool with which you can make it do just about anything you need. As there are multiple masterminds taking caring of Apache, it will remain the king of webservers for long!