Winhotspot - Winhotspot or "windows Hotspot" is a Free "WiFi hotspot" / "virtual WiFi Router" software. winhotspot is a virtual wifi router windows 7 or 8
pfSense - pfSense is a free and open source firewall and router that also features unified threat management, load balancing, multi WAN, and more
Connectify Hotspot - Connectify Me hotspot is a PC app that turns your computer into a Wi-Fi hotspot.
OPNsense - OPNsense® you next open source firewall. Free Download. High-end Security Made Easy™. Offers Intrusion Prevention, Captive Portal, Traffic Shaping and more.
IPFire - IPFire is a server distribution with intended to use as a firewall.
ClearOS - A very good alternative for Windows Server, for free