diff --git a/README.md b/README.md
index 4203006..37662ec 100644
--- a/README.md
+++ b/README.md
@@ -90,7 +90,7 @@ It's a great way to learn.
 * [**JavaScript**: _A cryptocurrency implementation in less than 1500 lines of code_](https://github.com/conradoqg/naivecoin)
 * [**JavaScript**: _Build your own Blockchain in JavaScript_](https://github.com/nambrot/blockchain-in-js)
 * [**JavaScript**: _Learn & Build a JavaScript Blockchain_](https://medium.com/digital-alchemy-holdings/learn-build-a-javascript-blockchain-part-1-ca61c285821e)
-* [**JavaScript**: _Creating a blockchain with JavaScript_](https://github.com/SavjeeTutorials/SavjeeCoin)
+* [**JavaScript**: _Creating a blockchain with JavaScript_](https://github.com/Savjee/SavjeeCoin)
 * [**JavaScript**: _How To Launch Your Own Production-Ready Cryptocurrency_](https://hackernoon.com/how-to-launch-your-own-production-ready-cryptocurrency-ab97cb773371)
 * [**JavaScript**: _Writing a Blockchain in Node.js_](https://www.smashingmagazine.com/2020/02/cryptocurrency-blockchain-node-js/)
 * [**Kotlin**: _Let’s implement a cryptocurrency in Kotlin_](https://medium.com/@vasilyf/lets-implement-a-cryptocurrency-in-kotlin-part-1-blockchain-8704069f8580)
@@ -98,7 +98,7 @@ It's a great way to learn.
 * [**Python**: _Build your own blockchain: a Python tutorial_](http://ecomunsing.com/build-your-own-blockchain)
 * [**Python**: _A Practical Introduction to Blockchain with Python_](http://adilmoujahid.com/posts/2018/03/intro-blockchain-bitcoin-python/)
 * [**Python**: _Let’s Build the Tiniest Blockchain_](https://medium.com/crypto-currently/lets-build-the-tiniest-blockchain-e70965a248b)
-* [**Ruby**: _Programming Blockchains Step-by-Step (Manuscripts Book Edition)_](https://github.com/yukimotopress/programming-blockchains-step-by-step)
+* [**Ruby**: _Programming Blockchains Step-by-Step (Manuscripts Book Edition)_](https://github.com/openblockchains/programming-blockchains)
 * [**Scala**: _How to build a simple actor-based blockchain_](https://medium.freecodecamp.org/how-to-build-a-simple-actor-based-blockchain-aac1e996c177)
 * [**TypeScript**: _Naivecoin: a tutorial for building a cryptocurrency_](https://lhartikk.github.io/)
 * [**TypeScript**: _NaivecoinStake: a tutorial for building a cryptocurrency with the Proof of Stake consensus_](https://naivecoinstake.learn.uno/)
@@ -180,7 +180,7 @@ It's a great way to learn.
 #### Build your own `Front-end Framework / Library`
 
 * [**JavaScript**: _WTF is JSX (Let's Build a JSX Renderer)_](https://jasonformat.com/wtf-is-jsx/)
-* [**JavaScript**: _A DIY guide to build your own React_](https://github.com/hexacta/didact)
+* [**JavaScript**: _A DIY guide to build your own React_](https://github.com/pomber/didact)
 * [**JavaScript**: _Building React From Scratch_](https://www.youtube.com/watch?v=_MAD4Oly9yg) [video]
 * [**JavaScript**: _Gooact: React in 160 lines of JavaScript_](https://medium.com/@sweetpalma/gooact-react-in-160-lines-of-javascript-44e0742ad60f)
 * [**JavaScript**: _Learn how React Reconciler package works by building your own lightweight React DOM_](https://hackernoon.com/learn-you-some-custom-react-renderers-aed7164a4199)
@@ -333,7 +333,7 @@ It's a great way to learn.
 * [**Java**: _Crafting interpreters: A handbook for making programming languages_](http://www.craftinginterpreters.com/)
 * [**Java**: _Creating JVM Language_](http://jakubdziworski.github.io/categories.html#Enkel-ref)
 * [**JavaScript**: _The Super Tiny Compiler_](https://github.com/jamiebuilds/the-super-tiny-compiler)
-* [**JavaScript**: _The Super Tiny Interpreter_](https://github.com/keyanzhang/the-super-tiny-interpreter)
+* [**JavaScript**: _The Super Tiny Interpreter_](https://github.com/keyz/the-super-tiny-interpreter)
 * [**JavaScript**: _Little Lisp interpreter_](https://maryrosecook.com/blog/post/little-lisp-interpreter)
 * [**JavaScript**: _How to implement a programming language in JavaScript_](http://lisperator.net/pltut/)
 * [**JavaScript**: _Let’s go write a Lisp_](https://idiocy.org/lets-go-write-a-lisp/part-1.html)
@@ -420,7 +420,7 @@ It's a great way to learn.
 * [**C#**: _Writing a Web Server from Scratch_](https://www.codeproject.com/Articles/859108/Writing-a-Web-Server-from-Scratch)
 * [**Node.js**: _Build Your Own Web Server From Scratch In JavaScript_](https://build-your-own.org/webserver/)
 * [**Node.js**: _Let's code a web server from scratch with NodeJS Streams_](https://www.codementor.io/@ziad-saab/let-s-code-a-web-server-from-scratch-with-nodejs-streams-h4uc9utji)
-* [**Node.js**: _lets-build-express_](https://github.com/antoaravinth/lets-build-express)
+* [**Node.js**: _lets-build-express_](https://github.com/antsmartian/lets-build-express)
 * [**PHP**: _Writing a webserver in pure PHP_](http://station.clancats.com/writing-a-webserver-in-pure-php/)
 * [**Python**: _A Simple Web Server_](http://aosabook.org/en/500L/a-simple-web-server.html)
 * [**Python**: _Let’s Build A Web Server._](https://ruslanspivak.com/lsbaws-part1/)
@@ -439,7 +439,7 @@ It's a great way to learn.
 * [**C**: _The very basics of a terminal emulator_](https://www.uninformativ.de/blog/postings/2018-02-24/0/POSTING-en.html)
 * [**C**: _Write a System Call_](https://brennan.io/2016/11/14/kernel-dev-ep3/)
 * [**C**: _Sol - An MQTT broker from scratch_](https://codepr.github.io/posts/sol-mqtt-broker)
-* [**C++**: _Build your own VR headset for $200_](https://github.com/relativty/Relativ)
+* [**C++**: _Build your own VR headset for $200_](https://github.com/relativty/Relativty)
 * [**C++**: _How X Window Managers work and how to write one_](https://seasonofcode.com/posts/how-x-window-managers-work-and-how-to-write-one-part-i.html)
 * [**C++**: _Writing a Linux Debugger_](https://blog.tartanllama.xyz/writing-a-linux-debugger-setup/)
 * [**C++**: _How a 64k intro is made_](http://www.lofibucket.com/articles/64k_intro.html)