There is an awesome article that goes over how one program can be written in different languages from the most abstract level of Math to Haskell to C to Assembly to actual machine code.
Tour de Babel - Funny de tour of programming languages.
Awesome static analysis - Static analysis tools for all programming languages, build tools, config files and more.
Twelf - Language used to specify, implement, and prove properties of deductive systems such as programming languages and logics.
GitHut - Place to discover languages on GitHub.
Programming Languages Zoo - Collection of implementations of miniature programming languages.
Semantic - Haskell library and command line tool for parsing, analyzing, and comparing source code.
Hello, World! - Hello world in every computer language.
TabNine - All-language ML autocompleter.
comby - Tool for changing code across many languages.
Quine - Self-referential program that can, without any external access, output its own source.
NEAL - Language-independent code analysis tool that aims to enable more people to write quality enforcement rules.
Mu - Minimal-dependency hobbyist computing stack (everything above the processor and OS kernel).
Bitsy - Best language to implement when writing your first compiler or interpreter.
codespan-reporting - Beautiful diagnostic reporting for text-based programming languages.
Hoist - Visual programming language inspired by Excel & Datalog.
Esoteric.Codes - Languages, platforms, and systems that break from the norms of computing.
Call-By-Push-Value - New programming language paradigm, based on the slogan “a value is, a computation does".
Zoekt - Fast text search engine, intended for use with source code.
PLaST research group - Focuses on applied programming languages and software engineering.
A Foundation for Typed Concatenative Languages (2017) - Presents a sound and complete type inference algorithm.
Analysis Tools - Most Popular Analysis Tools by Programming Language.
Polygott - Base Docker image for the Repl.it evaluation server.
teaberry - Learning project to implement a typed functional programming language/dialect of ML, which aims to be accessible and usable like Python is.
Langkit - Tool whose purpose is to make it easy to create syntactic and semantic analysis engines. Language creation framework.
remark-prism - Syntax highlighter for markdown code blocks using Prism.