You’ve come to the right place for help on content creation apps, as we’ve covered them pretty thoroughly over the last few years. It’s difficult to replace Photoshop with a free program, so don’t expect miracles.
That said, lots of folks use the open-source photo editor GIMP, which works on Windows, Mac and Linux, and has a lot of power for a free app. It’s not particularly streamlined, and you’ll need to download a RAW converter, but it can handle most jobs.
If you want to stick to the Adobe world and don’t mind taking a drastic drop in features, there’s Photoshop Express, which has the bonus of working on iOS and Android as well as Windows (but not macOS). Other options that favor simplicity over extensive features are Fotor and InPixio, both of which are free image editors with paid upgrades.
As far as audio editing software, many of us at Engadget use Audacity, which is versatile, surprisingly powerful, and works on both PCs and Macs. It’s especially handy and very widely used for podcasts and voice recording. Other good options are Ashampoo’s well-designed and easy-to-use Music Studio 7 and Ocenaudio, which has a streamlined interface and built-in filters.
You didn’t ask, but another key content creation category is video editing. I’m a big fan of Blackmagic’s Davinci Resolve 16, and have used it to edit multiple Engadget videos. It’s faster and better than Adobe Premiere Pro CC in many ways, though a bit harder to use, especially for color correction. If you can master it, though, the free version is fast and versatile, and you can upgrade to the full Studio version for just $300, no subscription needed.