I haven't found any software that does what Windows Media Center does, and, for that reason, consider it irrepplaceable, and I like it very much.
It doesn't appear that Plex provides live, over-the-air tv.
You're right it doesn't. I missed that in your earlier post. Check out Hauppauge.com
They have a USB TV tuner that will work with your laptop and software called WinTV that will probably do what you're looking for.
I've been looking at getting a 4 tuner Tablo Box that will integrate with my current PLEX/Roku setup. That will allow me to record multiple over the air programs while watching TV. Once recorded shows can either be streamed to me remotely over the web or if bandwidth is an issue I can drop the MP4 files onto a laptop or tablet to watch later.
As far as I can tell, Plex looks like a type of cloud service, where you can save videos etc. to a cloud and then access them whenever you have internet access via a hotspot.
Think of PLEX as creating your own version of Netflix and Pandora rolled into one running on a PC on your home network or in your boat.
After setting up our server I burned all our DVDs, Blu-Rays and music onto a 1TB hard drive.
I also burned TV shows from DVD, hi-res videos from YouTube and videos from places like Off Center Harbor.
I can watch these shows on a big screen via Roku or on any PC or tablet connected to the network (via an app). I can stream CD quality music to any device on the network by album, artist, genre or playlist.
I can open a hole through my firewall and stream any of these formats to a remote device. That could be watching a movie via a high speed connection at the marina or listening to my music library in the car over my cell phone connected to the AUX jack in the car stereo.
It takes a while to get everything loaded but it's pretty incredible once you do. I've rediscovered music I forgot I had. The next step is pulling all the old vinyl out and recording it
I started digging into all this when we cut the cord with cable. It's pretty amazing what you can do now.