There have been other free photography sites, but I can assure that I've not seen anything like this before. Sometimes a site will offer free downloads but when it came time to using those images you still needed to purchase a license. Alternatively, there are other sites that offer free downloads, but you need to attribute the original photographer a specific way. Of course, I'm okay with everyone getting the attribution they deserve, but my clients don't want some fine print at the bottom of each slide of their eLearning course.
Check out https://pikwizard.com/ when you get a chance. They're just starting out, but they already have over 100,000 completely free images, of which 20,000 are exclusive to them. They are updating their library of stock photos daily and have expressed to me that their goal is to have more than 1 million images.
One thing that is rare are free sites that include pictures of people. You see models are required to sign a release and it's difficult for photographers and photo sites to get photos of people for free distribution. Pikwizard.com has a lot of pictures of people. Check this out for yourself by searching their site for things like "office" or "meeting", and you'll find some great quality examples of these types of photos.
I asked Micheal Brennan from Pikwizard.com how can all these files be truly free?
Micheal explained that the photos on the site have two different licenses.
The first is Creative Commons Universal. Pik Wizard doesn't own the images but the people who do have waived the copyright and allowed the use of the photos. You can learn more about this type of license here: https://pikwizard.com/cc0-license.
The other license is where Pik Wizard owns the images but made them free to use without attribution. They still retain the copyright. You can learn about this type of license here: https://pikwizard.com/free-license.
Michael went on to explain that there are certain cases where an image can't be used, but in 99% of the cases, you will be free to use these photos for free without attribution. Each image will have an explanation on its page that covers these sorts of details.
Hope you find this useful.