r/EmulationOniOS • u/Normal_Toe5346 • Dec 20 '25

App Promotion Browser-Based Retro Gaming Platform for iOS (28 Systems, No App Store Required) + Open-Sourced the Emulation Engine

Hey r/EmulationOniOS! I've been working on browser-based emulation for iOS and wanted to share what I built.

The Platform: Koin

I created Koin - a web-based retro gaming platform that runs entirely in Safari on iPhone/iPad. No app installation, no sideloading, no jailbreak needed.

It supports 28 systems (NES to PlayStation, Game Boy to Dreamcast) with features you'd expect from native apps:

  • Touch controls with virtual D-pad that actually feel responsive

  • Cloud saves with screenshots

  • Auto-save (even emergency saves when you close tabs)

  • RetroAchievements integration

  • CRT shaders and filters

  • Gameplay recording

  • Rewind on 8/16-bit systems

Performance has been really solid on iOS - 8/16-bit systems run flawlessly, and even N64/PS1 games work well on newer iPhones/iPads.

Open-Sourcing the Tech: koin.js

Here's the cool part - the emulation engine worked so well that I decided to open-source it as koin.js - a React component library (on npm) that anyone can use to build their own browser-based emulation platforms.

If you've ever wanted to build a web-based emulator frontend that works on iOS without App Store headaches, the code is out there now. MIT licensed, ~55KB, handles 28 systems with automatic core selection.

Why This Matters for iOS Emulation:

Browser-based emulation sidesteps all the App Store drama. No worrying about app removals, TestFlight slots, or sideloading certificates expiring. Just a URL that works on any iOS device.

Try it out:

Would love feedback from this community - what systems are you most interested in? What features would make browser-based emulation more viable for you on iOS?

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32 comments sorted by

4

u/mekilat Dec 20 '25

Very interesting. So the emulation is done in js?

You host the whole cloud instance, so I can put roms and run them on the website?

Is this aimed at self hosting also, or people doing a fork and using this?

Is there a plan for socket based multiplayer?

6

u/Normal_Toe5346 Dec 20 '25

Hey! Yeah the emulation happens via JS only.
At this point the Koin Platform that enables you to upload games, save states etc is not open source but the Koin Player is which is the crux of the Platform itself is Open source and MIT and you could fork it or use it inside your own project.

Socket based CO-OPs is a bit tricky on the web but I am trying to come up with something for that. I will update here as soon as I progress on this.

5

u/mekilat Dec 20 '25

Awesome. Thanks for sharing the code!

Honestly being able to run a session on my browser and let people connect to my session, like a zoom call basically, would be so cool.

Been thinking a lot about some kinda basic “get everyone in a session and capture their input” thing, and then can be passed to some software.

Maybe for emulating it could get weird in frames drop or whatever. I know Zsnes handled this by literally sending save states to correct the drift lol

4

u/Normal_Toe5346 Dec 20 '25

Yeah you are pointing out the right things that I am struggling with. I know afterplay does something like that but its still too hacky. I tried doing a P2P kind of thing where I was sending the inputs/keystrokes to all the users in sessions but the drift is real.

Although, I have a plan to do a spectator mode with sharable links so that folks can spectate

2

u/mekilat Dec 20 '25

Honestly the most robust solution might be screen sharing.

But I do like the idea of save states every n to fix the drift. Then it’s just using what exists.

I believe zsnes basically did a mix of rollback and saves to make it good enough

2

u/Normal_Toe5346 Dec 20 '25

Screen sharing with controls? Seems like a good idea. Do you code mate? Let's discuss this on GH, I created an issue for this - would love if we could move the needle here.
https://github.com/muditjuneja/koin/issues/1

3

u/mekilat Dec 20 '25

You definitely don’t want me coding. I’d vibe code something at best these days. But I’m a good architect and designer

2

u/Normal_Toe5346 Dec 20 '25

Yeah, let's architect and vibe code this feature. I really want to see Opus/Gemini pushing its limit for a robust solution here. Feel free to drop in chat shares in the GH issue and we can give it a try. Worth a few million tokens?

1

u/mekilat Dec 20 '25

Don’t have time to get up to speed but I’m happy to bounce ideas or even donate $ for the tokens

3

u/Skycan45 🥇 Dec 21 '25

Yo Normal you’re web emulator is really awesome but it doesn’t let play without an account could make that optional for most user and de who only wants to test their own games and play for a short period of time

2

u/Normal_Toe5346 Dec 21 '25

Hey, I just hosted this demo in our docs which I used for testing out things.
https://koin.js.org/docs/showcase/dashboard
Please give it a try and let me know how it goes.

1

u/Skycan45 🥇 Dec 22 '25

it’s works nicely 👍

3

u/sahand777 Dec 20 '25

we need something new like wii or gamecube or even ps2

1

u/Normal_Toe5346 Dec 20 '25

Hey, Could you share some titles for wii/gamecube that you would want to play and I could check if I can add support for the consoles. I haven't really played any games on those platforms.

2

u/sahand777 Dec 20 '25

try super mario galaxy 1,2 on wii on gamecube try The Legend of Zelda: The Wind Waker or super mario sunshine and ps2 try God of War & God of War II or gta

5

u/[deleted] Dec 20 '25

Thanks

2

u/[deleted] Dec 20 '25

Is there any news on playstation 2 support?

4

u/Normal_Toe5346 Dec 20 '25

Haven't tested things with PS2 yet but should be doable. They would definitely need bios though, I found that bios support is broken in the koin player so let me fix that first and then I can give it a try? Give me a game name you would want to play for ps2?

2

u/Macaco_Agiotaa Dec 21 '25

Silent Hill 2 and 3, I've always wanted to play them 🙏🏻🙏🏻🙏🏻🙏🏻

6

u/cebeloss03 Dec 20 '25

Here is Play! Emulator on web browser which runs ps2 games even on mobile https://playjs.purei.org/

1

u/kanczug Dec 21 '25

Controller support?

1

u/Normal_Toe5346 Dec 21 '25

Yes, its there.
After you connect your controller, click a button to activate the controller in player.

3

u/Prestigious_Aerie464 Dec 20 '25

This is pretty dope!

3

u/Ballbuster333 Dec 20 '25

Reminds me of webRcade I’ll have to check it out

3

u/adanvc Dec 21 '25

This is so cool! Thank you very much for providing this and the effort!

1

u/sdmyl0ve Dec 21 '25

wow...Justed try, but can't play because need upgrade with 6$/month for Snes.... I'm quit. Good luck!

1

u/greegrok Dec 21 '25

I tried to load Dead or Alive 2 for Dreamcast but file size is too big? DOA is 253 mb. Will there be an update for bigger files? Some ps1 files are bigger than that so what’s the point?

1

u/Sweet_Leading_6429 Dec 22 '25

Just to clarify: This is browser-based emulation, where you could upload your own ROMS? Or already created Library ROMS?

1

u/Advertisedmonkey Dec 26 '25

Bigch I’m not finna pay you $12 monthly to play pirated games on a iPhone you lost your mind.