The asset store holds a vast array of good and not so good offerings, some free, some reasonable, and some just down right ludicrous.
Based on what we have covered in this book, the following are some prebuilt alternatives you can use if you don't want to roll your own; above all, they are highly rated and reviewed:
LeenTween isn't just a powerful tweening solution (a framework that will create transitions smoothly between two points, like animations), but it also has a very robust and easy-to-use messaging system bundled with it. It is available at https://www.assetstore.unity3d.com/#/content/3595.
For more details on how to use LeanTween or its event dispatcher (messaging), visit the DentedPixels website, http://dentedpixel.com/.
You might also find some other interesting topics there (my favorite being procedural textures scripts).
Tip
Also what's noteworthy on the store is a very in-depth review of all the competitor tweening solutions and the pros/cons of each. It is there at http://dentedpixel.com/video/leantween-speed-comparison-to-itween-and-hotween/.
Dialoguer is quite fantastic for the price and offers not only a full conversation and UI system, but also a rich node-based editing tool for crafting conversations. It is available at https://www.assetstore.unity3d.com/#/content/14854.
Another engine that is fairly full featured is called Conversation Engine. Similar to dialoguer, it has a node-based editor and UI features and includes video tutorials on its use. It can be found at https://www.assetstore.unity3d.com/en/#!/content/11967.
If you haven't had the time to build your own, it can be worth shopping around; remember that you can always extend what you get with the lessons you have learned in this title.
A great post as a rundown of the top editor extension assets on the store that is well worth a read is available at http://blogs.unity3d.com/2014/04/17/extend-the-editor-to-infinity-and-beyond/.
Managing multiple languages within your project can be a hassle, but as it turns out, there are assets to help you deal with this; the most notable one is Language Manager Asset. For full details, check out the author's post about the asset at http://thecreativechris.wordpress.com/2014/04/03/localization-support-with-unity/.
If you like Voxels (scenes made up of thousands/millions of tiny cubes) such as MineCraft, you might want to try out Cubiquity. It's a full Voxel engine that you can use to build your games with mountains of power as it's implemented in C++ and available at https://bitbucket.org/volumesoffun/cubiquity-for-unity3d.