It is bit limited now - everyone is going streaming now...
You can get TV tuner to pickup local (on air) stations or to get unencrypted TV stations from your cable provider. But that depends on your cable provider - if they provide anything at all and what. And none advertise the fact, that you can skip cable box...
Get network tuner - e.g., one of HDHomerun =
https://www.silicondust.com - I have two duals, so I have 4 channels I can record/watch at once. No need for drivers, OS version independent ;-) But that is just hardware - important to keep reading below for software...
Now, the trouble becomes media software. HDHomerun has its own application, but it is not that good (my opinion)... I had some success with Plex which is kind of easy to setup and generally works. It was one of the few I tested and eventually liked. The only missing thing I disliked was skipping back and forth in recording which was currently being recorded. In order to skip around you needed to wait until recording is finished.
For TV you need to pay monthly fee (small, few $ I think) - but if I recall correctly it includes program guide which is never free anyway.
It's bit weird logic - you have to run server, which interfaces with the TV tuner and other sources, like you own media (which are free to stream)...
Then you can watch in clients - including on that same computer or any other device - like other computer, iPad, iPhone, Android, etc. One server can serve many clients if network can handle it.
There are other systems, some for free, but there is no obvious dominating one. May be someone will provide better suggestion.
