Adobe ShockWave Player
If you want to play in online games on your browser, there's a good chance you'll need Adobe ShockWave Player, the daddy of online action plug-ins.
After a simple install and restart of your browser, you'll be able to enjoy a large range of graphically impressive online experiences. Most of the time you won't notice Adobe ShockWave Player is even there, but like flash and other plug ins it should be one of your basic downloads after installing a browser.
Compared to other more recent plug-ins like Unity, Adobe ShockWave Player is quite resource heavy. We tried some online Shockwave things that really slowed down our system. However, while it's a platform developers continue to use, it's useful to have.
While Flash and Unity have probably superseded it in many places, Adobe ShockWave Player can still give you some enjoyable Web gaming.