I would like to introduce GNU Enterprise (http://www.gnuenterprise). I think often is 'overlooked' because it appears so ambitious, but there are companies using GNU Enterprise for production critical applications today. We match almost all functionality of Oracle SQL*Forms (before they moved to java) and are getting more and more features daily.
We have one of the strongest visual IDE's for a framework that I have seen that lets you bind forms to over 15 databases, in a matter of minutes. The forms are completely cross platform (win32, motif, gtk, curses and soon html and mac) w/o any changes.
Here is our standard blurb. I think we will gain popularity as we start to release applications that are made from the framework, but as of today the framework itself is highly useful for writing applications.
GNU Enterprise (GNUe) is a suite of tools and applications for solving the needs of the enterprise. From human resources, accounting, customer relationship management and project management to supply chain or e-commerce, GNUe can handle the needs of any business, large or small. If you are looking for a full-function ERP, GNUe is the package for you.
Beyond applications, GNUe is a development framework that enables enterprise information technology professionals to customize applications for their businesses. The GNUe platform boasts an open architecture and easy maintenance. It gives users a modular system and freedom from being stuck with a single-source vendor. Plus, users get consistency and the ability to tap into a network of best practices from other enterprises, saving valuable development time.
GNUe is a Free Software project with a corps of volunteer developers around the world working on GNUe projects. This provides the added benefits of easy internationalization of applications. The project is working to provide a worldwide GNUe community, allowing everyone who is involved in the project access to other talented business information technology professionals.