You might be interested in Racoon[1], which is a desktop client (Java) for downloading apps from the Play Store, or into BlankStore [2][3], which is an alternative mobile client.

Both are FOSS projects.

[1] http://www.onyxbits.de/raccoon

[2] https://github.com/mar-v-in/BlankStore

[3] http://forum.xda-developers.com/showthread.php?t=1715375