News : Online tool for JavaScript and TypeScript

Using this online tool you can create a JavaScript/TypeScript project that runs natively on all your users' devices: web, android, iOS.

You can find more details and the documentation on the official page with the documentation.

An very old video example from 7 years ago, see the official youtube.

Here is a screenshot of this online tool I tested today:

The Ren'Py visual novel engine .

Ren'Py is a visual novel engine – used by thousands of creators from around the world – that helps you use words, images, and sounds to tell interactive stories that run on computers and mobile devices. These can be both visual novels and life simulation games. The easy to learn script language allows anyone to efficiently write large visual novels, while its Python scripting is enough for complex simulation games.

Ren'Py is free to use with commercial and non-commercial games and you can find on the official website.

This run's on Android 5.0+,HTML5/Web Assembly (Beta),Linux x86_64/Arm,Windows 7+,Mac OS X 10.10+ and iOS 11+.

This is last video tutorial from RenPy start tutorials but you can find more on web.

Thunkable : Create online mobile applications for iOS and Android.

Thunkable is the platform where anyone can build their own mobile applications for iOS and Android.
This online tool is free to use with a google account.
The Thunkable platform charges a maintenance fee for the use of certain components such as Ads by AdMob and Payment by Stripe.
You can start build your on an app is as simple as dragging and dropping your favorite components and connecting them together with blocks.
Learn how to make your first app from this video from official youtube channel:

The COLOR online tool.

This COLOR online tool help you to create, share, and apply color palettes to your UI, as well as measure the accessibility level of any color combination.
Select your color palette r create a custom one.
The next step is to export the output to Android , iOs or CodePen website.

Principle - the design tool for iOS.

This application is a Macintosh-based UX prototyping tool designed to design animated and interactive user interfaces.
You can choose a device preset or enter a custom Art board size to design for your favorite platform and then with few moves make your interactions and animations design.
You can find many video tutorials on youtube.
Compatibility: Requires iOS 9.0 or later. Compatible with iPhone, iPad, and iPod touch.
Let's see one example from Principle Repo youtube channel:

Allegro 5 library for game development.

Allegro 4 and Allegro 5 are cross-platform, open source, game programming libraries, primarily for C and C++ developers.

The Allegro library provides low level routines like input, graphics, midi, sound effects, and timing.
It is cross platform : Windows, OS X, Linux, DOS, and others.
The official website is here.
You can find some tutorials, and various articles for beginners.
Other information can be found here.