Thanks to @Arcnor, Pixel Dungeon is now available for playing on PC/Mac/Linux! Please consider, that the desktop version is still in beta state. Also, not all features, available in Android version, may be implemented on desktop platforms.

Here is some additional information:

• Currently the desktop version is based on v.1.7.2a, i.e. it's one version behind Google Play. It will be updated.
• The desktop version is not an exact copy of the mobile one. For example, keyboard support was added.
• In mobile version some actions can be performed with long tap. In desktop version they can be performed in a similar manner with long click. Alternatively, you can use ctrl + click.
• ...

• Java application: desktop-1.7.2a-1.jar - 10.6 MB
  It runs on any system, but you need to have Java installed. Java is a rather common thing, so chances are it's already installed on your computer. If not, you can download it here.
• Windows bundle (no JRE required): win-1.7.2a-1.zip - 46.3 MB
• Mac OS X bundle (no JRE required): coming soon