SQLcl is the new command line tool from Oracle, more specifically from the SQL Developer team. It is currently an Early Adopter (EA) release and you can download it from: http://www.oracle.com/technetwork/developer-tools/sql-developer/downloads/sqldev-41ea-2372780.html

After testing it for a while I was hooked and plan on using it as a full time replacement for SQL*Plus (which I think is the intent of the product).

The only difficulty I had was where to store it on OS X so it was accessible everywhere. Here's how I "installed" it and hopefully this will be useful for others:

cd ~/Downloads
#Note: version/filename of file will change for each release
unzip sqlcl-4.1.0.15.067.0446-no-jre.zip

#Assuming you already have an /oracle directory (I had one for the instant client)
cp -r sqlcl /oracle

#Give sqlcl execute permission
cd /oracle/sqlcl/bin
chmod 755 sql

#rename to sqlcl so no confusion (optional)
mv sql sqlcl

#Add directory to path so can run anywhere in the command line:

#Temporary access:
PATH=$PATH:/oracle/sqlcl/bin

#Permanent access:
#Note: See Barry's comment below about storing in /etc/paths.d on Mac
vi ~/.bash_profile
#Add just above the export PATH line
PATH=$PATH:/oracle/sqlcl/bin

In the above example I installed SQLcl in the /oracle directory. You could also put it anywhere you want such as /usr/local/oracle etc. Just make sure that you reference the location in the PATH environment variable.

If you're looking for more info on SQLcl as well as some excellent examples check out Kris Rice's blog and Jeff Smith's blog.

Update: The following article covers how to create login scripts for SQLcl.