Reactive Programming has been gathering steam lately, and for good reasons - it has real value. Here are some things to know about Reactive Programming.
Spreadsheet cell formulas are the best example of reactive logic - cells react to changes in the data they reference - automatically. This is a branch of declarative programming where you focus on what the system should do, not how.
Microsoft has made this technology available in Rx. It has met with favorable response, now in use for example in Twitter.
Espresso has made this concept available for backend database business logic.
The automated "reaction" logic can replace immense amounts of code. The most familiar example is the oft-lamented "cocktail napkin specification", wherein 5 simple statements require hundreds of lines of coding in traditional non-reactive (imperative) code.
Reactive turns this entire economic upside down, by providing the "Executable Cocktail Napkin". You simply specify the logic, and it is executable. In an industry where 20% improvements are significant, a 100X reduction is quite extraordinary.
Agility gets a similar boost, since changes can be made without worrying about logic ordering. Ordering is the main cost component of traditional programming, requiring significant analysis for each change. Reactive logic is automatically ordered based on dependencies, as in the familiar spreadsheet example.
Traditional code is error prone since it must not only be correct, it must be called. Reactive logic is automatically applied to all changes - it's the next level up in reuse beyond Object Oriented Programming.
Business Users can read Reactive Logic - it's automatic documentation. This means they can partner with IT to spot errors and reduce Requirements Risk.
Reactive does not solve all problems. One of the key technical challenges is providing speed of Reactive along with the power of traditional programming. A corollary is that the traditional programming integration should ideally be with a familiar, widely using language.