On the AADL site, via their Tool Integrators, Toolsets, TOPCASED pages I ran across an interesting presentation about TOPCASED, which at the beginning basically says that with the lifetime of aerospace products running as long as 10 to 30 years no company is able to commit to supporting a development tool for such a long time at an acceptable cost. (I think this was essentially explaining their motivation for developing TOPCASED as an open source project, though it's not quite explicitly stated.)
I find this very interesting, since I've worked on a number of projects that, although not in the aerospace arena, have had lifetimes vastly exceeding the expectations of anybody involved on the project. While some of the original design and development tools are still available, some are not, and replacing them, or in some cases just using the ones that are still available, can be a complicated business. For small projects, collecting all the tools under CM so as to be able rebuild any version of the project with the original tools can be prohibitively expensive when commercial software is involved. The idea of using open source tools because those will still be available in 20 or 30 years and can be supported in a cost-effective way seems reasonable, so it's interesting to see that there are a number of open source projects of this nature in aerospace, an arena known for mission critical systems.