An amazing project from a talented Czech Programer Ivan Kutskir. It comprises over 100,000 lines of code! This is an online program that you can run in your browser, with a photoshop-like interface with all the things you would expect. It doesn’t have all the bells and whistles. It works with some RAW formats though the raw processing is fairly basic – you get basic exposure adjustments then it converts to a PSD file that you can edit. However if you want, you could always use one of the more capable RAW converters (RawTherapee, DarkTable, or even Adobe Camera Raw (yes you can download that for free)). It features layers, blending modes, lots of filters, selection tools…. All for free (well almost. You “pay” by having a set of adverts flashing on the right hand side of the page – there is a paid option that removes the adverts).
If you use Chrome browser (or similar) you can “install” Photopea as an App so you can run it entirely from your computer without an internet connection. (I guess if you then turn off your internet, you can edit your photos without adverts popping up).
Here is one person’s review https://fixthephoto.com/photopea-review.html and another https://irvkrick.com/photopea-review-a-free-photoshop-alternative-that-works-in-your-browser/