Generic rules for detection and validation are:
1. We do our best to detect what is installed on user's machine: vagrant, virtualbox, java and do not detect cdk, cygwin, or DevStudio;
2. When version is detected it must be verified against the range of what we believe valid versions; it might be defined as a set or condition.
vagrant: minimal and tested version is 1.7.4, all newer releases are good to continue with warning except 1.8.0 which is known to have networking problems;
virtualbox: minimal and tested 5.0.8 and all newer releases are good to continue with warning;
jvm: minimal and tested is 1.8 and all newer releases are good to continue with warning;
3. For vagrant and virtual box if detected version is out of the range, installer shows error message with explanation and doesn't let go any further until detected version is uninstalled, which should be done manually and then installer should be restarted; If nothing is detected included versions can be installed or installer could be configured to use specific location;
4. For JVM if not supported version is detected, included one can be used or installer could be pointed to right location to use.
5. When location for required software set manually installer try will try detect version and verify it using (2);
6. When version cannot be detected and manually selected location looks like required install, installer should let to proceed with warning.

It would be great if the installer allowed the user to use some of the required tools they have already installed.

The idea is to detect if the dependencies are already present and let the user decide if they want to use them, or install new ones. Also, it could let the user select the tools themselves if they want to use a different installation than detected, etc.

The confirmation page we currently have looks like the place to put all this, since it already displays most of the stuff that is going to get installed. Anyway, I have tried to modify it and squeeze the controls in and this is how the selection turned out (imagine the messages looking a bit smarter):

nivologd@gmail.com & crobson@redhat.com, what's your opinion on this?