To some extent, they did extend the universe. There is a couple of series of comics that tell detailed stories of the team before, during, and after the timeline shown on TV. Plus a few novels too.

But truthfully speaking, nothing holds a candle to an actual TV show.

I use TVDown.co - it's a website you can customize to add your shows, and it picks them up from TVMaze. There isn't an option to track what shows you've watched or haven't yet, but it suits the purpose I want it for: to show up which shows are coming up next, that too in my time zone's time.