你不认识这玩意不重要，先看完下面这段视频你也许就会有点明白了。
youtube的，速度可能慢了点。

简介：

Phun 2D Physics Sandbox is free for non-commercial use (see license). Phun combines physics and art in a playful way with open ended undirected gameplay. Phun is not just a game - it is much more! Phun is educational, entertaining and pretty addictive! To learn Phun easily and quickly, read this getting started tutorial. If you have problems, please read the FAQ or ask for help in the forums. There are lots of great examples in the media section, including the original Phun video, which is very instructive. There are also and lots of scenes you can download for free from Phunbox.
You'll need a decent computer with hardware 3D (well, 2D) acceleration. Remember, Phun is still beta, so it still has a few glitches.
To learn what is new in the latest version of Phun, see the changelog. We hope you enjoy Phun and spread the word to your friends!

大概的中文简介，上面的可以无视了。

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作者网站：http://www.phunland.com/wiki/Home （恩，国内的别费力气了，不开代理是连不上的，伟大的GFW啊。）

还是让我给出下载链接吧：
Windows Phun beta 4.22 installer (2.62 MB) – recommended for Windows XP and earlier
Phun beta 4.22 zip archive (3.65 MB) – recommended for Windows Vista – extract to a directory with write access (such as My Documents or the desktop)
Linux Phun beta 4.22 for 32-bit Linux, tar.bz2 archive (3.05 MB)
Phun beta 4.22 for 64-bit Linux, tar.bz2 archive (2.99 MB)
MacOS Installation: Double click the downloaded file to mount it. Open the mounted disk image (found on your desktop) and copy the Phun folder to your Applications directory.
Phun beta 4.22 (7.42 MB) – for Mac OS X 10.4 and later, works on both x8

下不了的看这吧，反正我是能下。
For Vista
For WinXP and earlier
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玩的愉快。

Technorati : phun, 游戏, 物理学