Top 7 declarative-language Open-Source Projects

nix

193 7,418 9.9 C++

Nix, the purely functional package manager

Project mention: What are the best resources to get started with nix? | reddit.com/r/NixOS | 2023-01-30

The nix website is in my bookmarks as well https://nixos.org/.
vega-lite

7 3,989 9.4 TypeScript

A concise grammar of interactive graphics, built on Vega.

Project mention: 2022 FIFA World Cup finishing position probability per team [OC] | reddit.com/r/dataisbeautiful | 2022-11-20

The underlying data is from an online betting site. Data analysis was done in Python and I used Vega/Altair for the visualisation.
Sonar

www.sonarsource.com
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Kaitai Struct

21 3,287 7.3 Shell

Kaitai Struct: declarative language to generate binary data parsers in C++ / C# / Go / Java / JavaScript / Lua / Nim / Perl / PHP / Python / Ruby

Project mention: What projects are you working on or planning to do this year? | reddit.com/r/C_Programming | 2023-01-07

Speaking of reading binary data, later I found Kaitai Struct. You can write file format in YAML, then it would transpile it to different programming languages. Highly recommend it if all you need is to read (it can not serialize data back to binary). There's even a web IDE to play with files, which is quite fun.
ring

3 1,033 9.9 C

Simple and flexible programming language for applications development (by ring-lang)

Project mention: Fifteen different implementation for the random user application using the Ring programming language (Console, GUI, Qt3D, RayLib, Web, Templates, MVC, etc.) | reddit.com/r/programming | 2022-09-30
logtalk3

26 332 9.7 Prolog

Logtalk - declarative object-oriented logic programming language

Project mention: Logtalk 3.62.0 released | reddit.com/r/prolog | 2023-01-31
Kyrix

0 135 0.0 JavaScript

Interactive details-on-demand data visualizations at scale
ascent

1 127 10.0 Rust

logic programming in Rust (by s-arash)

Project mention: Datafrog: A lightweight Datalog engine in Rust | news.ycombinator.com | 2022-11-13

I think people should look at Ascent [1]. I love the way it embeds Rust seamlessly. It's like JSX for Datalog/Rust.
[1]: https://github.com/s-arash/ascent
InfluxDB

www.influxdata.com
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NOTE: The open source projects on this list are ordered by number of github stars. The number of mentions indicates repo mentiontions in the last 12 Months or since we started tracking (Dec 2020). The latest post mention was on 2023-01-31.