MuGo

made by brilee, submitted by davidbalbert
A minimal Go AI modeled on AlphaGo. It became the basis of Minigo (https://github.com/tensorflow/minigo), which is maintained by the Tensorflow team.

bidict

made by jab, submitted by porterjamesj
Bidict not only provides high-performance, industrial-strength bidirectional mapping data structures for Python, but it includes a shocking amount of computing joy to boot. Take a closer look at bidict to illuminate some of Python's lesser-known and more under-appreciated darkest corners, and discover a few surprises along the way.

Palette Town

made by quelledanielle, submitted by davidbalbert
A GameBoy Color palette browser that uses your webcam.

systemf

made by Andrew Yoon, submitted by porterjamesj
An extension of the brainfuck esoteric programming language that adds support for linux syscalls, and an example HTTP server written in it.

LeetCode Pairing

made by Douglas Lerner, patrick_mccarver, submitted by Douglas Lerner
A Chrome extension which enables coders to pair program over the internet and solve LeetCode.com algorithm coding challenges together. Users can type into a shared text editor and video chat in real time, all in the browser. Recursers can login using their Recurse.com account. Source Code: https://github.com/MerkleBros/leetcode-pairing-chrome-extension

Zip 3

made by proxpero, submitted by porterjamesj
An extension of the Swift standard library's `zip` function to three lists.

Line Rider

made by davidlu, submitted by porterjamesj
A remake of the classic flash game using modern web technologies. You can see the source code for the physics engine here: https://github.com/conundrumer/lr-core

Unicodots

made by BrennanC, submitted by porterjamesj
The asciidots visual programming language, plus emoji!

Ray Tracer written in Kotlin

made by JonathanOliveira, submitted by porterjamesj
A ray tracer written in Kotlin, completely from scratch with no libraries.

Type systems and logic

made by trillionalyssa, submitted by jollysonali
A long form essay that shows the relationship between type systems and logic systems in type theory.