A lot of free and paid forum software has a download plugin. I am not sure whether a gallery plugin will be enough in your case.
WordPress would definitely have a Downloads plugin. But I would check out of the league CMS like October CMS, Grav etc because WordPress is getting hard to manage with all the updates. It is no longer fit it and forget it . There will be some amount of maintenance, plugins might break and so on.
If you do not want to try anything fancy, Joomla too might be a good option