The Oracle 11g Release 2 (188.8.131.52) Database Instant Client for Apple OS X on Intel x86-64 is now available for download from OTN. It is supported on the two latest OS X releases: Lion (10.7) and Mountain Lion (10.8). It provides both 32-bit and 64-bit client support.
Oracle Instant Client is a simple bundle of libraries that client tools and programs (like PHP and Ruby) can link with. This allows those tools to access Oracle Databases.
Any issues with Instant Client can be posted to the OTN Instant Client Forum.