There are many aspects to consider when building a game. This requires a lot of knowledge, skills and time to build and integrate all the components. 
Fortunately the Unity 3D platform has a great selection of packages and assets to accelerate the build of tools, models, shaders, sound effects, animations etc. 

For the development of Math it Right 3D Adventure I’ve used the following Unity packages.

Unity Technologies Assets

Addressables by Unity Technologies. The Addressable Asset System allows the developer to ask for an asset via its address. Once an asset (e.g. a prefab) is marked “addressable”, it generates an address which can be called from anywhere. Wherever the asset resides (local or remote), the system will locate it and its dependencies, then return it. 

Cinemachine by Unity Technologies. Smart camera tools for passionate creators.  

Input System by Unity Technologies. A new input system which can be used as a more extensible and customizable alternative to Unity’s classic input system in UnityEngine.Input. 

Post Processing by Unity Technologies. The post-processing stack (v2) comes with a collection of effects and image filters you can apply to your cameras to improve the visuals of your games. 

Terrain Tools. The Terrain Tools package adds additonal terrain sculpting brushes and tools to your project to help create stunning terrain assets and ease the workflows. 

TextMeshPro. TextMeshPro is the ultimate text solution for Unity. It’s the perfect replacement for Unity’s UI Text and the legacy Text Mesh. 

Timeline. Use Unity Timeline to create cinematic content, game-play sequences, audio sequences, and complex particle effects. 

Universal RP. The Universal Render Pipeline (URP) is a prebuilt Scriptable Render Pipeline, made by Unity. URP provides artist-friendly workflows that let you quickly and easily create optimized graphics across a range of platforms, from mobile to high-end consoles and PCs.

Third Party Tools

I’ve also used the following Unity Store Assets: 

Dreamteck Splines by Dreamteck 

Dreamteck Splines is designed to feel  like a native part of Unity, leveraging familiar tools and interfaces. It is both designer and programmer-friendly allowing for quick prototyping and implementing of unique behaviors. Focused on flexibility, ease of use and performance, it is suitable for both small, medium and large-scale projects. 

Feel by More Mountains 

Feel is the best way to improve your game’s feel and make it extra juicy. Packed with more than 100 feedbacks. It’ll let you easily trigger screenshakes, animate transforms, play with sounds, cameras, particles, physics, post processing, text, shaders, time, UI, and so much more. 

HUD Navigation System by Sickscore Games 

HUD Navigation System (HNS) is the ultimate collection of the most common navigation concepts from various games. HNS is modular so you can easily disable features you don’t need (unused features don’t affect the performance). 

Odin – Inspector and Serializer by Sirenix 

Odin puts your Unity workflow on steroids, making it easy to build powerful and advanced user-friendly editors for you and your entire team.  

Text Animator for Unity by Febucci Creations 

Bring your dialogues to life, animating your game texts with this easy to use and customize plugin. 

Third Party Controllers

Kinematic Character Controller by Philippe St-Armand 

Character Controller a relatively low-level character controller solution that is not tied to any specific game genre. It integrates into any project/architecture with as little friction or bloat as possible. Instead of using rigidbody physics, it uses a “collide and slide” algorithm that makes its movements perfectly fluid, precise and responsive. Note that its “kinematic” nature means that it will not get pushed by forces or rigidbodies automatically. These sorts of interactions have to be explicitly scripted. 

Third Party Visual Effects

Flat Kit: Toon Shading and Water by Dustyroom 

The custom shading model is versatile enough to work great for classic cel/toon shading and for unique styles of experimental projects. 

Highlight Plus by Kronnect 

Highlight Plus is a powerful asset that adds outline, glow, overlay, see-through and other effects to any 3D object in your scene.

Confetti FX 2 by Archanor VFX 

The asset also includes a new confetti-rain type emitter, as well as extra confetti textures, normal maps, documentation and more. Standard and URP support. 

Epic Toon FX by Archanor 

Epic Toon FX is a huge collection of 930 cartoony particle effects. Standard and URP support. 

Third Party Models

Low Poly Animated Animals by Polyperfect 

High quality rigged low poly animals with amazing animations, stunning demo scenes, multiple textures, sounds and Wander Script. 

Tiny Dragon by Suriyun 

Tiny dragons models.