Adobe Flash / SWF
What Flash was
Adobe Flash (originally Macromedia Flash, and before that FutureSplash Animator) was a multimedia authoring platform and browser plugin for playing vector animations, interactive applications, and games embedded directly in web pages. Its native file format, SWF (commonly pronounced "swiff", short for ShockWave Flash), packaged vector graphics, bitmaps, sound, video, and a scripting language called ActionScript into a single compact file a browser could stream and play.
Flash mattered because, for most of its life, it was the only practical way to put animation, sound, and real interactivity on a web page. HTML in that era had no native video element, no canvas, and only limited scripting through early JavaScript — Flash filled all three gaps at once with one authoring tool and one plugin.
Origins
The technology began as FutureSplash Animator, a small vector-drawing and animation tool. Macromedia acquired it in 1996 and relaunched it as Macromedia Flash, pairing a timeline-based animation editor with a lightweight runtime that most users already had installed, or could install in seconds, because it shipped bundled with major browsers and operating systems for years. Adobe acquired Macromedia in 2005 and the product became Adobe Flash.
How it worked
A Flash file was authored in a dedicated tool (or, for programmers, produced by other toolchains that targeted the SWF format directly) and compiled to a single .swf file. The browser plugin, Flash Player, parsed that file and rendered it inside a rectangular region of the page. Because everything was vector-based, animations stayed small in file size and scaled cleanly to different sizes, which is a large part of why Flash suited the slow, metered internet connections of the early 2000s so well.
ActionScript, the scripting language bundled with Flash, let authors go beyond animation into full interactivity: menus, forms, and eventually entire games and applications, some of which were more capable than what was possible in a browser using JavaScript alone at the time.
What it was used for
Flash's uses stretched far beyond "internet cartoons," though it did make internet animation into its own popular art form (see Newgrounds). It was also the standard way to embed video before native browser video existed — YouTube's original player was a Flash application — and it was the technology behind the enormous ecosystem of embeddable browser games that portals like the ones described in Flash game portals were built around. Banner ads, whole marketing sites, and business applications were built in it too.
Decline and end of life
Flash's decline had several causes at once: a string of security vulnerabilities in the plugin made it a favourite target for attackers; Apple's decision not to support Flash on iOS removed it from the fastest-growing class of devices; and the standards HTML gained through the 2010s — native video and audio elements, canvas, and much faster JavaScript — eventually did in an open, plugin-free way most of what Flash used to do alone.
Adobe formally ended support for Flash Player at the end of 2020, and the plugin was built to actively refuse to run Flash content from the following January — not just go unsupported, but stop working outright. That single cutoff is covered in its own detail at The Flash shutdown of 2020. Content authored in the format did not disappear with it, though: projects like Ruffle and archives like Flashpoint exist specifically to keep decades of SWF content playable without the original, now-unsupported plugin — which is also why this catalogue can run games at all.