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How to set up a local development environment for Celo using Mac.
While many commands will be the same, you may need to follow the instructions for your specific OS when installing software. The Celo docs have some resources for Windows development.
Before building on Celo, you need to set up a development environment to make sure you have the proper tools to build an application. This setup includes a combination of general development tools, Celo specific tools, and mobile development tools.

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Web2 Prerequisites

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Xcode

Xcode is Apple’s integrated development environment for macOS, used to develop software for macOS, iOS, iPadOS, watchOS, and tvOS. While Xcode falls under the Celo Prerequisites, Xcode takes a long time to download, which is why it is first on this list. It’s best to start this download first, or even start downloading it before going to bed (depending on your internet connection).

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Node, NPM and NVM

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Node

Node is a JavaScript runtime that allows you to execute JS code outside a web browser. It is an open-source server environment and runs on various platforms.

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NPM

npm stands for Node Package Manager and is the world’s largest software registry. npm is what you’ll use for installing published JS packages. npm comes bundled with Node, so you won’t need to install it separately.

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NVM

nvm stands for Node Version Manager. Different projects often require different versions of Node, and nvm makes it easy to switch between those versions. This is recommended if you plan to develop a lot of JS-based applications and npm also recommends nvm. For Windows users, there are nodist and nvm-windows.

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Install Node and npm via nvm

curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.40.0/install.sh | bash
Verify the installation by running: 
command -v nvm
which should output nvm. You can now install Node with nvm install <version>.
You can switch node versions using
nvm use <version>

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Homebrew

Homebrew is a way of managing packages on macOS. Install Homebrew 
/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"
Get the latest packages 
brew update

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Yarn

yarn is a package manager similar to npm. For the most part, they do the same job and projects will let you know in the README or package.json which package manager they recommend using. Usually, you can use either or, but you should not use both in the same project. Running the Celo Development Blockchain requires yarn, so you can install it now.

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Install yarn

Option 1: Since you already have npm installed, you can use it to install yarn 
npm install -g yarn
This will install the Yarn global binary.
The -g is short for --global. This flag means you are installing this package on your system and it will be accessible from the cli no matter what project you are in.
Option 2: Install yarn with Homebrew 
# Update brew if you haven't recently
$ brew update

# Install yarn
$ brew install yarn

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Expo

Expo is a framework and a platform for universal React applications. It lets you build mobile applications for both iOS and Android while using the same JavaScript/TypeScript codebase. This means that you don’t need to be a “mobile developer” to build mobile apps!

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Install Expo

Since you already setup npm, you can now install the expo-cli package. 
npm install -g expo-cli

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Docker

Docker is an application focused on build and deployment tools. It allows developers to build and share containerized apps. Rather than making the developer manually install a bunch of packages, a dev can just download a Docker image and start it and all the application installation and setup will be taken care of for them.

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Install Docker

You might need to install Docker Desktop for your OS. Once you’ve done that, you can access docker via your cli. 
docker --version

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Celo Prerequisites

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Local Development Blockchain

See Local Development Chain w/ Protocol Contracts for how to get started with developing on a local test environment.

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Celo CLI

The Celo CLI is a command-line tool for interacting with the Celo Protocol smart contracts. Some of the things you can do with it include looking at accounts, checking balances, and signing transactions. Install Celo CLI 
npm install -g @celo/celocli

... # lots of logs

+ @celo/celocli@x.x.xx
added x packages from x contributors in x.xs
Installation can take over a minute, so be patient depending on your internet connection.

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iOS

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Xcode

Xcode allows you to build and deploy the Celo Wallet. If you do not have an iOS device, Xcode can emulate one. To install this, you need an Apple Developer account (free), but you don’t need to be part of the Apple Developer Program (costs money) to download Xcode. Install Xcode Download Xcode from the Apple Developer website. It is massive (10.6 GB), so we will start this first so it can be downloaded while we do everything else. Once this is done downloading, install it. Cocopods, Bundler Navigate to the iOS directory of the mobile package (/celo-monorepo/packages/mobile/ios) and run the following to install cocoapods and bundler. 
# install cocopods and bundler if you don't already have it
$ gem install cocoapods # you might need to run with sudo if this fails
$ gem install bundler

# download the project dependencies
$ bundle install

# run inside mobile/ios
$ bundle exec pod install
If your machine does not recognize the gem command, you may need to download Ruby first.

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Android

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Java

Java allows you to build and deploy the mobile app to Android devices. Install Java Install by running the following: 
$ brew install cask
$ brew tap homebrew/cask-versions
$ brew install homebrew/cask-versions/adoptopenjdk8

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Android Dev Tools

Install the Android SDK and platform-tools 
$ brew install android-sdk
$ brew install android-platform-tools
Next, install Android Studio and add the Android NDK.
These paths may differ on your machine. You can find the path to the SDK and NDK via the Android Studio menu.
export ANDROID_HOME=/usr/local/share/android-sdk
export ANDROID_NDK=/usr/local/share/android-ndk
export ANDROID_SDK_ROOT=/usr/local/share/android-sdk
# this is an optional gradle configuration that should make builds faster
export GRADLE_OPTS='-Dorg.gradle.daemon=true -Dorg.gradle.parallel=true -Dorg.gradle.jvmargs="-Xmx4096m -XX:+HeapDumpOnOutOfMemoryError"'
Then install the Android 29 platform 
sdkmanager 'platforms;android-29

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Android Emulator

For the same reason you installed the emulator iOS (you may or may not have an Android device), you can also install the Android emulator. Install Emulator Manager One Android emulator option is Genymotion. 
brew install genymotion
Under OSX High Sierra and later, you’ll get a message that you need to approve it in System Preferences > Security & Privacy > General. Do that, and then repeat the line above. Then make sure the ADB path is set correctly in Genymotion — set Preferences > ADB > Use custom Android SDK tools to /usr/local/share/android-sdk (same as $ANDROID_HOME)

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Extras

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Solidity support for VSCode

Solidity support for VSCode (or your preferred IDE/text editor) Celo smart contracts are written in Solidity. While Solidity syntax is very similar to JavaScript/TypeScript, there are some differences and JS syntax support will not like Solidity files. Installing an extension on your IDE will be a big help as you develop smart contracts.