On this site you will find information about SQLTools++, which is based on the original open source tool SQLTools (http://www.sqltools.net). SQLTools is a Windows frontend for Oracle databases and offers a quite powerful text editor and result set browser, along with numerous other useful tools, like schema/object browser and DDL extraction tools. You can find more information about SQLTools on the original home page. Although it is far from being as comprehensive as other tools available like TOra or TOAD, it has its unique features, and in addition to that it is lightweight (The installer is just about 1MB in size), fast and does not need an installation, so you can run it directly from any storage medium like an USB stick, which makes it a good choice as quick access tool if you come to a new place and need to quickly check database related issues. All you need is a valid installation of an Oracle client and your copy of SQLTools. 

The version available on this site offers some additional functionality and enhancements which I found to be useful. Most of the features added/modified are about better handling of the tool and better support of SQL statement performance tuning. You'll get instant support for many features Oracle provides in that area with a single click (e.g. DBMS_XPLAN.DISPLAY_CURSOR output for 10g and later, and an emulation of that functionality for 9i), which makes SQL tuning much easier.