I'm also interested to know what everyone is using!

For painting walls, most of the major paint manufacturers have color visualizer tools where you can upload a photo of your house and "paint" the walls different colors. The tricky part is defining the various areas--"wall", "trim", etc. The software will make a guess, but if a section of the house is in shadow, you'll have to manually identify the area..It's not terribly difficult if you have familiarity with software drawing tools.

For other types of design collages, I use Olioboard, which is an online tool designed for exactly that. You can grab pics from many shopping websites using a browser add-in, and the software is pretty good at stripping white or black backgrounds from images so that you can put a virtual lamp from one site on a virtual table from another site. The basic membership is free; I think paying $ gets you fancier imaging tools. https://olioboard.com/

Some people use Photoshop Elements (I think it's called). I use an old version of Microsoft paint, but it has very few automatic functions so I don't recommend it unless you are already familiar with it. Very luddite of me, but it's an old friend.