Drizzle is a (currently interpreted) programming language designed as something I would like to use, and used as a way to learn lots of new things.

Monkey interpreter in C#, from the book Writing an Interpreter in Go

Lox interpreter in Python - based on the book "Crafting Interpreters" by Robert Nystrom

C++实现的tree-walking类型玩具解释器 (thanks: Robert Nystrom)

Yet another Python implementation of Lox programming language

Simple tree-walking interpreter for the "rinha de compiladores" challenge