Skeleton can be useful if you want to add a responsive grid without using a heavy framework like Bootstrap.
It appears that the project has been abandoned on GitHub. The last commit by the author was on 2014-12-29. As of 2016-02-19 there are 46 issues and 36 pull requests with no apparent response from the author. 
There are at least three forks of Skeleton currently:
- Includes utility class names prefixed with
u-, which are parsed as microformats.
- gRegor Morrill uses it on gregorlove.com since 2015-07-12.