A single checkbox isn't very clear on purpose. Perhaps a button styled similarly to the delete button could be added instead?

When scrolling through list items, the scroll bar appears on top of them. The list items should have a little empty space to their right to fix this.

Add support for Skin Manager. This should include installing and deleting skins, along with viewing previews of their main textures.

Mockup of textures page, with user hovering over the first skin

How the user gets to this page is still to be thought of. Perhaps each car that skins are installed for act as dropdowns revealing the installed skins.

Pretty self explanitory

Custom sounds from ZSounds should be able to be played back in the content manager. The settings page should contain an option to control the playback volume. When a sound the played, the "Play" button should change to a "Stop" button and stop the sound if clicked again.

Add support for Cargo Swap. Implementation should be basically the same as Skin Managers.

Deleting the main group deletes the whole mod. Not sure what people would expect to happen when deleting it, but it shouldn't be allowed

When opening the application with the DV installation directory not set, or set to something invalid, no other pages should be accessible, and an alert that the install dir needs to be set should be shown.

When playing sounds from ZSounds, they "Play" button should turn into a "Stop" button and allow the audio to be stopped.

Alerts to signal when an action failed (or succeeded?) should be implemented. These could be implemented similarly to Psst, as that would work fairly well with the small window size. Perhaps there could be a limit to the maximum amount of notifications shown on screen at once, not allowing it to take up more than half, or three-quarters of the window size.

Some refactoring may have to be done to ensure error messages are useful and contain the appropriate amount of information to fix the issue or ask for help.

Add support for Zeibach's Sounds.
This should include support for installing and deleting cars. Further functionally will be added later.

Add an option to customize the theme of the application.

When switching the mod you're currently looking at, there's a period of a few seconds where the whole application freezes. This isn't caused by the application re-scanning the file system for mod info, as the update functions aren't called and the data remains out-of-date if changes are made. The duration of the freeze appears to scale with the number of list items preset, so that's probably a good starting point.

Most likely the same issue as jpochyla/psst#255

When going to the page of a mod that isn't installed, there should be a little warning stating that it's not installed and pointing to a download link. We should be able to open the browser to that link when clicked using open-rs.

A confirmation dialog should appear before deleting content, with a settings option to disable it. This can simply be an alert that never goes away, with confirm and cancel buttons.

If Derail Valley is running, the application should show a warning and not allow the user to perform any actions until it's closed. This could possibly use the same confirmation dialog as the delete confirmations, but without any buttons to close it.