NethServer is a great performer for SMEs and can provide email, gateway, firewall, etc and host Websites. It really is a highly configurable system, and in our business, has replaced other hardware completely.
You can install applications specific to your industry sector, from the Software Center or other sources.
NethServer does not limit the type of application you can have; decide on the application that best suits your business needs, install it and then use it. For example, installing Wordpress gives you a website with so many templates there is probably one that may match your business perfectly.
Our own experience shows it is capable of supporting 10-15 users on modest hardware with less than 4Gb RAM.