Alternatives to Silverlight
Because Silverlight 4 can run inside or outside of the web browser, its alternatives cover a wider landscape. Interestingly, though, not many technologies allow you to program just once but run on multiple platforms and in multiple modes (offline/online, in the browser/out of the browser). In that sense, Silverlight is pretty unique.
In the Web Browser
Silverlight is traditionally a connected application running within a web browser. In that field, the landscape didn't really change much since Silverlight 2, with the exception maybe of XHTML, which is barely mentioned anymore and considered already obsolete now that HTML5 is becoming a trending topic.
This is the obvious contender, the one technology that is most often mentioned when Silverlight is compared to other frameworks. Adobe Flash is installed on a huge number of computers and various operating systems. It is also a well-known environment, and many companies develop applications in Flash for the Web.
As mentioned when Silverlight 2 was released, Flash is not going to be killed by Silverlight, and in fact this was never Microsoft's intention. Rather, Silverlight provides a welcomed alternative to firms who do not want to invest in two very different technologies for the desktop and the Web. In that sense, Silverlight is a great choice because it is developed with the same languages and the same tools as the well-known Windows Forms, ASP.NET, and WPF.
DHTML and AJAX
This new revision of HTML intends to provide a wide range of rich functionality, allowing developers to reduce the use of third-party plug-ins. In this matter, it positions itself as a concurrent of Adobe Flash and Microsoft Silverlight.
Although it is true that plug-ins cause problems, they also solve some. One big issue with HTML is that different web browsers have different implementations of the standard. This is a well-known issue: Testing a web page for all major web browsers on all major operating systems can be a real hassle. On the other hand, Silverlight as a plug-in is guaranteed to run the same in every supported web browser. It is the old "write once, run anywhere."
The major issue that HTML5 faces is that a wide adoption will take a lot of time. Also, if we learned anything from the past, it is that each browser is likely to offer a slightly different feature set. Some features will simply be missing from some browsers; other features will be implemented in a different manner. Compatibility will take a lot of time, if it is ever achieved. In the meantime, and until we know whether HTML5 really delivers what it promises, Silverlight offers a real alternative.
Out of the Browser
Running a Silverlight application out of the browser is similar to running a desktop application. Therefore, Silverlight can be seen as an alternative to any desktop technology, including "classic" MFC and Windows Forms applications on Windows or Mac applications on Mac OS. Let's just take a look at two modern desktop technologies.
Windows Presentation Foundation
When Silverlight functionalities are not enough to accomplish what you want, the answer is probably to look into WPF, Silverlight's "big sister." Even though the convergence is always greater between these two technologies, and Silverlight becomes richer and steps on WPF's playground, there are still some scenarios for which Silverlight is not suitable.
The biggest disadvantage of WPF with regard to Silverlight is that it runs only on Windows systems. Also, it requires the complete .NET framework (instead of the Silverlight subset), which is larger and takes more time to install on the target machine if it is not already present. Finally, although WPF is richer than Silverlight, this richness also makes it more complicated to learn. It is easier to start with Silverlight.
Note that thanks to the combined efforts of the Silverlight team and the WPF team at Microsoft, the compatibility between both technologies has never been greater, and it is in fact possible to convert a Silverlight application to WPF with a large portion of shared code. Generally speaking, however, and because Silverlight is a subset of .NET, it is easier to start in Silverlight and extend the application to WPF than the contrary. Similarly, it is also easier to start learning Silverlight and then to move to WPF.
A less well-known platform developed by Adobe is called AIR and allows creating desktop applications. As such, it is not a concurrent of "in-browser" Silverlight, but rather of the out-of-the-browser applications.
For users, AIR applications are known to be heavy in memory consumption, and require an additional framework that must be installed the first time you run an AIR application (even if you have Flash already installed). This can be a problem on corporate networks, where IT departments are often reluctant to install new components on users' PCs. Silverlight, on the other hand, is installed once and gets the out-of-the-browser capabilities immediately.
Some technologies are still running inside some web browsers, but are becoming obsolete with time. The two mentioned in this section are not the only ones, but they are the best known, and it is possible that a developer starting a new project will be asked to consider these in the variant analysis.
Java as a plug-in is quite widespread and allows small applications known as applets to run in the web browser. Java was revolutionary in that way when it was released, but it suffers from a lot of issues:
- Java is notoriously slow. It's slow to install on a new computer, and especially slow to start.
- Java applets have a bad reputation when it comes to security. This claim might not be as true in newer versions as it used to be, but Java's adoption in the corporate world has suffered a lot from this concern.
- Java is cumbersome for .NET developers. The tools and the language are unusual and require additional training.
Silverlight addresses these concerns and offers a convincing alternative to Java applets. Perhaps the most compelling argument is that Silverlight is .NET. If your developers already know .NET-based client application technologies (WPF, Windows Forms, ASP.NET, and so on), they will feel at home very fast with Silverlight, and have a solid foundation to build on.
Similarly to Java applets, ActiveX controls were once very popular to enrich a web page, but are rendered pretty much obsolete nowadays by the many improvements made to new technologies, and especially Silverlight. If you are a developer or maintainer of ActiveX controls, it is probably time to consider moving to the newer, richer, and safer platform that Microsoft is developing. ActiveX controls suffer from the same problems as Java applets regarding security and restrictions in the enterprise world; in addition, they run only on Windows-based operating systems, which prevents a large user base from using them.
Silverlight differs significantly from ActiveX, and converting existing applications to this new technology is not the easiest task a developer can dream of. With this step, however, you will offer a newer, richer, and much friendlier interface to your users, and make a big step toward the future of software development.