Top 5 realtime-game Open-Source Projects

nakama

40 8,278 9.0 Go

Distributed server for social and realtime games and apps.

Project mention: Game Server Framework Recommendation | /r/golang | 2023-07-09

nakama: https://github.com/heroiclabs/nakama

colyseus

16 5,485 9.3 TypeScript

⚔ Multiplayer Framework for Node.js

Project mention: Need advice on what to learn in order to develop a multiplayer web-based game. | /r/webdev | 2023-07-06

If you don't want to dive deep into backend then https://colyseus.io/ might also be an option.

SurveyJS

surveyjs.io sponsored

Open-Source JSON Form Builder to Create Dynamic Forms Right in Your App. With SurveyJS form UI libraries, you can build and style forms in a fully-integrated drag & drop form builder, render them in your JS app, and store form submission data in any backend, inc. PHP, ASP.NET Core, and Node.js.
openspades

6 1,098 2.9 C++

Compatible client of Ace of Spades 0.75

Project mention: Open source Diablo 1 engine – DevilutionX 1.5.0 released | news.ycombinator.com | 2023-06-17

Ace of Spades is one. I usually play with the OpenSpades client[1], but there is also Betterspades[2], and probably many other clients I don't know of yet. There are usually about 10-50 players online on the public servers listed on BuildAndShoot[3], variable depending on the time of day and mostly from Latin America it seems.
One can host the game with piqueserver[4]. I'm not sure if one can still host with the original Ace of Spades server, but the game was 'shut down' in 2019 so maybe not.
[1]: https://openspades.yvt.jp/
[2]: https://github.com/xtreme8000/BetterSpades
[3]: https://www.buildandshoot.com/servers/
[4]: https://www.piqueserver.org/

NazaraEngine

1 660 9.8 C++

Nazara Engine is a cross-platform framework aimed at (but not limited to) real-time applications requiring audio, 2D and 3D real-time rendering, network and more.
ab-server

18 52 0.0 TypeScript

2d multiplayer action game server for Node.js based on WebSocket communication.

Project mention: Current status | /r/airmash | 2023-07-08

The code is an open source, https://github.com/wight-airmash/ab-server

InfluxDB

www.influxdata.com sponsored

Power Real-Time Data Analytics at Scale. Get real-time insights from all types of time series data with InfluxDB. Ingest, query, and analyze billions of data points in real-time with unbounded cardinality.

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 2023-07-09.