Lyman E Bertsch needs to run an application on a relative's computer. Installing the program isn't an option. Can Lyman run the program off a flash drive?
Probably not. But you may be able to find another program that does the same thing, but that you can run off a flash drive.
We call these programs portable, because they can be easily moved between computers and don't need to be installed. You can carry these on a portable storage device, such as a flash drive, and run them on any Windows PC. And you would be amazed how much portable software is out there.
A lot of portable programs are diagnostic or repair-oriented in nature. This allows you to take your flash drive to the home of a friend or relative with a misbehaving PC, plug it in, and diagnose their sick computer. For some suggestions in this area, go to the article The Bootable Maintenance Flash Drive, and scroll down to the heading "Extra Tools for Your Flash Drive."
Use a search engine to find a portable program that does what you need. Search for the word portable, along with the type of software; for instance, portable genealogy software.
I used that example because Lyman specifically asked about genealogy software. I found several, two of which seemed to have good reputations: Gramps Portable and ScionPC. (I have no experience with genealogy software, so please don't consider these to be my personal recommendations.)
And here's something else you might consider: PortableApps. This free portable program organizes and helps you launch other portable programs. You can install other portable programs into PortableApps (and no, that doesn't involve installing them into Windows). Then launch the programs from inside.