ScreenshotMaker is small java applet used to generate uniform Play Store screenshots with titles and descriptions with minimal effort.
I've only just gotten this thing to work on my laptop, so I have no idea what the requirements are. I have tested it a little on Windows, and although there are a few issues (all file chooser dialogs go to System32, and none of them restrict the file extensions like they're supposed to), it seems to be usable.
Creating a Desktop Entry
On most versions of Linux, you can create a desktop entry that will appear in whatever version of start menu your desktop environment uses by going to "file -> create desktop entry" and waiting for the ridiculously ugly confirmation dialog to appear. If you have followed instructions like these to set up a fingerprint sensor as an alternative to entering your password for the sudo command, you may need to swipe your fingerprint before the dialog will appear. I don't know why this happens. I don't know what I'm doing. I'm bad at things.
Simply enter a title, description, pick your colors and other preferences, choose a 16:9 screenshot to put in the frame, and hit "export image" to choose a location to save your screenshot.
You can save sets of preferences as ".sm" files for easier use in the future by going to "file -> save as", then "file -> open" when you next want to use it.