I recently set up a new MacBook Pro for development and installed some developer tools like Java and Maven.  After checking out my source code from Subversion and building it using Maven a folder with the name tilde (~) appeared in the same directory as my source code.  I deleted the folder and a little while later I noticed it was back.  After some digging around I found that setting the path of my local maven repository in my settings.xml file so it started with a ~ for my home directory was the problem.  Every time I ran a build it was trying to put a new local repository in a tilde directory of the working directory.  After updating the path to use /Users/{username} it stopped creating the tilde folder.