It is available on the website, from GitHub and from the Launchpad Project Tracker. The package will install Open Rails on your Windows PC.
If you already have Open Rails installed, then set the Options > Update mode to Stable (recommended)

and look out for the Update to 1.4 link, which is refreshed every day.

Clicking the link will upgrade your current version to v1.4.
A list of new features and changes is also available on the website and from GitHub.
There is also a 4-minute video on YouTube which introduces them.
Finally, a big thank you to the guys that make this possible; admins, coders, testers, bug reporters and our hosts,
here at Elvas Tower (thanks, Dave) and at UKTrainSim.