Aptana is being developed and distributed under the EPL (Eclipse Public License), which means the binaries and source code are being made publicly available for free. What's more, the EPL allows developers to take EPL licensed software, build proprietary add-ons or modifications, and redistribute them commercially and royalty free. The EPL is much more liberal in that sense than the GPL and it amazes me that a tool as incredible as Aptana is being given away so freely. Aptana is still a beta product, though, so maybe plans for a commercial version will emerge with time. I hope they do because this development team is doing great work.
My words can do little justice to the Aptana project, so I encourage you to check out their site (which itself is amazingly well constructed!) and see Aptana firsthand. If Aptana remains a free product once it leaves beta, I think it could easily stand second only to FireFox as one of the best looking and most useful Open Source projects ever created.