One feature that rolled out with Unity 4.5 is the module manager. The module manager is a new system for us to be able to deploy updates to specific parts of Unity without making a complete Unity release.
Let’s say that Google releases an amazing new phone, but it requires a small change to Unity’s Android support in order for Unity to properly support it. With the previous release model, we need to gather changes for a bugfix release, perform a full automated and manual quality assurance pass over Unity and all platforms, potentially publish some release candidates, and then publish a new version of Unity, installer packages larger than 1 GB each, for everyone to install and upgrade their projects.
With the module manager system, we can quickly make a single change, test only the Android support module for regressions, and publish a new 15MB Android support module for download on demand.
In Unity 4.5, we’re beginning by supporting updates to Android, BlackBerry, iOS, and Windows Phone 8 as modules.
We're still fine-tuning the module manager system, so there aren't any automatic update notifications yet in Unity 4.5. When we publish a module update, we'll announce it via our usual communication methods: forums, social media, potentially a blog post. At that point, the module manager window will show an available update for the module in question. Click the "Download" button, restart Unity once the download finishes, and kapow! -- your updated module is installed and loaded in Unity.
In upcoming versions of Unity, we'll continue developing and extending the module manager by adding modular update support for more platforms (the goal is to eventually support updating all our platforms this way), as well as support for updating other Unity subsystems, for example the upcoming Unity GUI system. Additionally, we plan to begin stripping these things out of the base Unity installer, in order to provide you with a smaller Unity download and a faster Unity installation, along with the ability to download and install support for the platforms and subsystems you care about. Other planned module manager features include: automatic update notifications, ability to switch between multiple installed module versions, support for pausing/resuming/restarting module downloads, and more.