An interesting requirement that came up for one of the applications I'm working on. We support both ClickOnce deployment for the majority of customers and traditional deployment with an MSI (WiX) package for those customers that require more control over the install process. 

However, regardless of how the application is installed, when a user clicks the 'Launch' button on our website, I need it to launch the application. If it's already been installed via the MSI package for the current user, it should launch the currently installed copy; otherwise, it should install/update/run the ClickOnce package. I suppose I could make the ClickOnce version launch the MSI-installed version if it's present, then quickly close. [This question](https://stackoverflow.com/questions/18885131/microsofts-application-installer-launches-my-clickonce-application) gives me hope that it might be possible by simply making both applications have the same GUID, but I'm not sure how to do that, or if it's even a good idea. 

It's trivial to make a link that launches the ClickOnce application:

```
<a href="/path/to/myapp.application">Launch</a>

```

And it's not too difficult to make a custom [protocol handler](https://msdn.microsoft.com/en-us/library/aa767914.aspx) that gets registered with the MSI:

```
<a href="myapp:launch">Launch</a>

```

However it [doesn't seem possible](https://stackoverflow.com/questions/7334460/how-can-i-associate-a-custom-url-protocol-with-a-clickonce-app) to make the ClickOnce application be able to handle this new protocol, and even if I solve that problem, this won't work for new customers that don't have either installed.

Is there a relatively simple way to make a single web link that will launch an MSI-installed application *or* a ClickOnce application?