ApexMate is a plugin for the awesome OSX text editor TextMate. Using the plug-in you can easily save apex code to your Salesforce.com account, run tests etc.

You can download a prebuilt version of the plug-in from the Downloads area, to install unzip the file, which should leave you with Salesforce_com.tmbundle and move it to ~/Library/Application Support/TextMate/Bundles and enjoy.