Those were the days: Have you ever found yourself missing the old Macintosh days? There's an app for that, and it comes from the most unlikely source—Slack. Well, at least from one of its creators.

Felix Rieseberg, a senior staff engineer at Slack, has developed an app that emulates Mac OS 8. The software runs on current iterations of macOS as well as Windows and Linux operating systems.

The app is called "macintosh.js." The ".js" suffix is appropriate, since the entire program is written in JavaScript. It is essentially a virtual machine that emulates a 1990's pre-PowerPC era Macintosh Quadra 900 equipped with a Motorola processor. The Quadra 900 was launched in 1991, so we're stepping back almost 30 years.

You won't find it on Apple's App Store because Cupertino bigwigs have not approved it. However, Rieseberg made the files and resources available on GitHub "for educational purposes only." Whether his disclaimer is enough to keep Apple's lawyers off his back remains to be seen.

The app includes several old software packages that one would have found for Macs of that era, including Photoshop 3, Premiere 4, Illustrator 5.5, StuffIt Expander, Apple's Web Page Construction Kit, and others.

A handful of preinstalled game demos come with it, which Rieseberg culled from an old 1997 MacWorld Demo Disc. Remember those? The classic Oregon Trail makes an appearance as does Duke Nukem 3D, Civilization II, Alley 19 Bowling, Damage Incorporated, and Dungeons & Dragons.

In addition to what comes preinstalled, Rieseberg says that any compatible software from that timeframe is installable (if you can find them). It can also mount disk images and transfer files from your current drive into the virtual Macintosh. Although the app includes Internet Explorer and Netscape Navigator, the emulator cannot connect to the internet.

Macintosh.js is not Rieseberg's first program to simulate old operating systems. His GitHub page shows that he also has a JavaScript Windows 95 emulator that also runs on all current computing platforms. Both are pretty cool to mess around with, especially if you have never seen what we old-timers used to use 30 years ago.

Ah, the nostalgia.