Look in the link I provided above (
PVR (wiki)) and the ones from it on the wiki.
It depends on what you want to do. If you already have an IPTV provider then something like IPTV Simple can handle that.
If you want live TV from an aerial or dish, then something like TVHeadend or one of the others can be a solution, but that's where you need the hardware to go with it to translate the signal into something digital on your network so that the backend can capture and handle it.
Personally I have two HDHomerun boxes fed by a roof aerial, and those feed a TVHeadend server running on my NAS box.
But there are several other options which you can see in the
PVR & Live TV Support section of the forum. Which one is appropriate for you and your needs is down to you to decide. But with the exception of IPTV Simple, all need hardware of some sort, and of course all require some source of media (either an aerial, a dish or an IPTV provider).