Unity 3D single build for various projects

Hi

I need to develop a single Unity3D standalone build for separate project modules.

Consider, I have various projects related to 'Physics' for the 12th grade, which contains separate models, images and their respective functionality. For example, Project1: 'Optics', Project2: 'Electrostatics', Project3: 'Dual Nature of matter' and so on. All of these projects are independent of each other in terms of functionality and are complete on their own. Now, I create a 'Unity build'(say, for android initially) that contains a menu layout along with hyperlinks to download separate projects aforementioned from a server. The requirement is to allow the user to download a project(Say, project1: 'Optics') jar/build out of many projects available as an extension/addition to the previous 'Unity build'(even if the size of the build already installed might increase on device). As soon as the project is downloaded, the user should be able to run the project module over the 'Unity Build' instead of running a separate application. Similarly, when the user is done with the downloaded project module(Project1: 'Optics'), another project module(say,Project2 : 'Electrostatics') can be downloaded from the menu of the build which will run over the same 'Unity Build'. The 'Unity build' application serves as an interface which can add a separate layer of encryption so that the projects cannot be downloaded over and run separately by any unrestricted user. Somewhat similar to a media player which can play various kinds of video files. However, in this scenario, I need to run various project modules.
I am looking to create builds for different platforms - Android, Windows, iOS and Web browser (if possible) with similar functionality.
Any kind of help will be appreciated

Thanks!

 

https://docs.unity3d.com/Manual/AssetBundlesIntro.html

 

Like Ostwind has said, what you can do is to create asset bundles for each of the "projects" that you mention here. Btw if would be a good idea to use some other name for these like modules or something because in Unity the word project is already used for something.
You can easily accomplish what you want using asset bundles which basically are packages created using Unity for assets in Unity. You should consider creating scene bundles with which you can bundle an entire scene in to a bundle.

Lastly even with this approach you cannot share asset bundles across different hardware platforms.