There are many games that have dropped which I'd love to purchase. Some PaulTheTall has already ported and so I can purchase them and port them with ease. Others are already on Mac so it's a matter of just downloading. However nowadays I noticed there are a lot of games I want that aren't available for Mac such as D4: Dark Dreams Don't Die, Ronin, Terraria, The Witcher 3 and Trine 3. How would I go about getting them on Mac via this site? Is it possible? Do I need to put a wish for them in the Wishlist?

There are also many games on here which I know already have Mac ports but they aren't available for some reason such as The Walking Dead, Sam and Max, Back To The Future and The Wolf Among Us. How would I go about requesting them? Would they go on a Wishlist as well?

i played back to the future on mac, looking forward to trine 3

Yep, for both questions you would need to create a wishlist, or check if there is already a wish for it and get people to vote ;)

This might persuade GOG to implement them in their library.

EDIT:

https://www.gog.com/wishlist/games

Mac versions for Ronin and Terraria should be coming soon. Creating wishlist entries is always a good idea and keep in mind to inform people when you've created one because that will get you more votes.

Some ports produce rights issues if the port was done by someone other than the developer. Sometimes devs have issues that prevent their porting what they had planned (Wadjet Eye's most recent, Trine Enhanced).

From the other end of the spectrum some devs promise to bring Mac then abandon their plans to port despite selling the game as "mac soon" (Ether One). Some devs put a Mac version on Steam and ignore GOG (Lovely Planet).

Contact the devs if you know of an existing port - twitter is a good place to do this, their website probably has a forum or at least contact info for the indies. Most of them should be less idiotic than the Lovely Planet dude.

There is Wine or Parallels.

And then there is Windows. Personally I've just gone with the latter option - I owned a bunch of Windows only games before having a PC available for gaming (thanks a lot, Insomnia Sale). Now I game on my MBP when possible, otherwise XP, 7, and eventually 10. All I do on Windows (at home) is play games. Everything else I do on my Mac and all 12TB of my various backup drives are formatted OSX.

re: the wishlist... There may already be something for "bring more mac & linux". I'm not sure you'll be able to get a ton of votes for a mac version of a specific game, but if pointed out, I'll vote. :)

Do note that the Mac version of Terraria hasn't been released anywhere yet, though it (along with the Linux verion) is apparently supposed to come out later this month. The Witcher 3: Wild Hunt's Mac port is also not out yet, though you can bet it'll be released here as soon as it's ready, since the publisher is a sister company to GOG. No version of Trine 3 will be out till this fall.

I strongly suspect that for the more recent GOG games that have Mac versions being sold elsewhere, but not here, there are some behind-the-scenes exclusivity deals in place that keep them locked into Steam (or wherever). Due to NDAs, GOG probably wouldn't even be able to say why they couldn't offer the Mac version, only something like "due to complex issues, it's unavailable at this time :( ."

But, yeah, as you surmised, and Goodaltgamer confirmed, the community wishlist is probably the best place to voice your desire for more Mac games in general on GOG. And, as he mentioned above, check for existing wishes before starting your own. Lots of duplicate wishes just dilute the vote counts. ; )

Thanks everyone! Is there any way to search through the Wishlist to see if someone already posted it or not? I noticed whenever I try to do one that's already been uploaded they usually put me on that one already so I can vote but I think they do that by using the web address I put in.

Also how would I notify everyone?

Here's the GOG site "Features" wishlist showing wishes with "mac" in the title (note the search bar on the left side).
Here's the same thing for the games wishlist.
Vote on what you want, add anything else that's not already there. : ) I have no idea what that sentence is supposed to mean. Notify everyone of what? If you mean "notify everyone of my wish on the wishlist", then this, right here, is how. Start a forum thread on the topic. Done! Achievement Unlocked! : P
If you want to (politely) get on GOG about it, send Support a "feedback" message. If you really want to go all in, of course, you could also go the tfishell route and try to get ahold of various developers and publishers on your own to try to get them to release their games (in your case, Mac versions specifically) here -- or at least get an ETA on when their Mac ports might be done. But that may be a bit more than you had in mind. =D

System Preferences -> Security & Privacy -> General -> Allow apps downloaded from - select anywhere (or maybe identified developer might be enough)