If you are looking for a Photoshop replacement, you really need to check out GIMP. It will feel very familiar if you already known Photoshop. It has a great online community for tutorials and learning from others. This isn’t just available for Mac, it is also available for Windows and Linux. https://www.gimp.org/

If you are looking for an Adobe Illustrator replacement, you need to check out Inkscape. It is very similar but has some unique variances. One example is that Inkscape’s native format is SVG (so if you incorpate graphics into web design SVG is supported natively in HTML5). This isn’t just for Mac, it is also available for Windows and Linux. https://inkscape.org/

I personally haven’t found a free alternative to Adobe Indesign that I use myself, however, I do know many people recommend Scribus. However, I don’t have any personal experience with it. It is also available on Mac, Windows and Linux. https://www.scribus.net/

If you are looking to do some 3D animation or 3D modeling (game design, illustration, blueprints and architecture), I highly recommend Blender 3D. Again it is available across platforms for Mac, Windows and Linux. It has been awhile since I’ve used it but it is just as powerful as programs like Autocad or Maya. https://www.blender.org/

I haven’t really found an open source or free alternative to Adobe Preimere or After Effects (Video Editing and Post Production software). So if anyone does have good recommendations for that, I’d be happy to hear about them.

Other notable mentions:
If you are looking for something quick that has a decent amount of functionality I would recommend checking out Canva.

If you don’t necessarily need free, some great low budget design software is Affinity. They have a Photo (Photoshop) offering, Designer (illustrator) offering, and Publisher (Indesign) offering currently. To buy each program (to own not to pay monthly) it is roughly $49 US per program - and all 3 are available for Mac and Windows to my knowledge. They also offer Photo and Designer for iPad each at $19 US. I’ve used these programs and am really liking them so far.

One other interesting tool is Figma, there is a free version that is still pretty robust. It is a vector based program (similar to Illustrator), but it has active collaboration so you can co-design in real-time or collaborate with other roles while you are brainstorming.

If you have questions or want to discuss in more detail, feel free to send me a message.