With Microsoft eventually phasing out their Small Business Server and pushing people to move to the cloud, there are alternatives out there that businesses can use.
The first is the SME server. This is open source and is a community-supported SME server. It is available as a downloadable ISO that can be downloaded and installed in under 20 minutes. Linux based, it can provide a host of services and can integrate Windows, Mac and Linux Clients within a network environment.
The second possibility is Point Clark Networks ClarkConnect. This is designed for a small/medium-sized network and has a huge list of options and integrated features that are easy to configure, as it has a web-based interface. Based on the Platform CentOS it can externally host and manage DNS Services, content updates, security updates as well as many other features.
Third in the list is Collax Business Server, which offers an all in one server for the use of basic networks that deal with file, mail, firewall and DHCP-Servers. If the idea is to put all of your services onto one server then this is simple and easy to manage. There are three editions available, Standard, multi-functional and a messaging and collaboration edition.