Lets start with Kodi, this is a client only type HTPC that requires a bit of networking knowledge if media files are stored on NAS drives. The best features about Kodi is its ability to playback nearly any file that you can throw at it and is only limited by the hardware in which it has been installed on.
Kodi can be installed on Mac OS, Windows, Linux and Android and can render different playback results. My personal favorite is Openelec Kodi, which is an embedded version of Kodi and only Kodi and this is a great option for a dedicated theater room
Plex is a break away version of Kodi (XBMC) with a server \client setup, the better the server hardware the better client experience. It can be installed on multiple type devices and is included in a lot of Smart TV and BluRay Players.
It has the ability to trans-code the payback file to suite the destination device.
Please note that Plex has a Pay version for it to work on all devices.
Windows Media Center! This is the one that started it all for me many years ago with probably the best PVR application even in the early days of Windows XP and limited to only two TV tuners it simply just worked. What it failed in was the ability to play back various files via the Media Center Extenders and had no ISO support but it recorded and playback live TV like no other. It has come to EOL with Windows 8.1 the last version of Media Center but I my self still use it every day as my PVR and main viewer in the lounge room and thanks to a great server feature called ServerWMC I can use it as my backend to watch Live and Recorder TV via Kodi, so where ever there is a Kodi, I can watch TV, Live or Recorded