While not a "Windows program," Ninite allows you to queue up and download a lot of the most common software installs you'd make after a fresh install.
In terms of actual windows programs, I quite like "Everything." It's basically a database of all the files on your computer that allows for near instant searching.
"Space Sniffer" is an excellent utility for finding what takes up a lot of room on your drive.
"Unidentified flying raw" is a free program that allows the manipulation and conversion of raw picture files. I use it before editing in Gimp, but if you have Photoshop, it's not necessary.
"Dark Table" is an acceptable free light room alternative if you have the patience. It's pretty slow though.
"Everything" is amazing. Works great as a search tool, and it has really cool capabilities. Lately I've been using to mass-rename files, instead of downloading a specific tool for that (or learning bash).
That program is essential windows software since the stock windows search utility is basically fake. There's no way to actually search without it.
Also I found a new good use for it recently. You can sort the entire file list by date and it updates live. So suppose you're using a program and it saves a file without telling you where. Since it's Windows and the file system is obfuscated to shit, there's no way to know where it is. But it will be near the top of the Search Everything file list.
Do not delete the Ninite exe. If you want to update all your apps later at once, just double click on the. exe again and Ninite will download & update all the installed apps and skip those that don't have any updates.