If you've heard of Cactus, you've probably heard some of our propaganda. You've then also probably heard some rumours about Cactus. Some may be true, some may not. We want to take this space to clarify some misconceptions.

1. Cactus is free software. Therefore, when I use Cactus, my code will be publicly available to everybody.

   No, it won't. Cactus applications are structured into modules, called thorns, and each thorn is a separate entity. Many thorns are available publicly under the LGPL or GPL (two public licences), but what you do with your thorns is completely up to you. Many people have private thorns, and so do we.

2. There is a company that sells Cactus. They will go closed source and leave all users stranded.

   That won't happen. There are currently so many research institutions with an interest in Cactus that they could keep it alive, even if CCT withdrew. And the Cactus licence (LGPL) means that no one can take Cactus away from you.

3. The Cactus home page hasn't been updated in quite some time. Cactus is a dead project.

   No, it isn't. We tend to update certain technical pages (e.g. about visualisation tools) much more often than the main page. The documentation in CVS is also regularly updated, although the copy on the web page may be outdated. You can check our CVS mailing lists for the gory details.

4. I've asked a question on the mailing list, but nobody answered.

   Impossible. Check the archives whether your message went through.

   Okay, so maybe we missed it. Please ask again -- we're usually pretty good about answering, but we are only human.

5. I've reported a bug / requested a feature, but you've completely ignored me. You are not interested in the common Cactus user.

   Yes, we are. Cactus development is mostly driven by application needs, i.e., by scientists who use Cactus to do research. Unfortunately we don't have money for programmers who just add features for other people. If you need something done in Cactus, you can either (1) explain to us in how far we need that feature ourselves -- then we may implement it, or (2) do it yourself -- we'll be happy to help you, or (3) help write a research proposal that funds a student or a programmer to implement what you need.

6. Cactus is developed in a closed room. You don't look for outside input, and there is no Cactus community.

   Well, Cactus development may be less open than GCC, but it is more open than Microsoft Word. Since most of us Cactus developers know each other personally, we discuss not only on mailing lists, but also in person and in conference calls. We find that personal communication simplifies human interaction a lot. That this leaves no public paper trail is sometimes a disadvantage.

   In general, Cactus development is based on meritocracy. That means, the more you contribute and the more presence you show on the mailing list, the more weight your word carries. If you just listen, you may miss certain discussions. If you give comments, you will stay more in the loop.

   Most discussions are held on the mailing list <developers@cactuscode.org>. We actually came to know a lot of interesting people on this list.

7. Cactus is used only at AEI and CCT.

   No, there are many more users. See e.g. <http://scholar.google.com/scholar?q=gr-qc+cactus> for a list of recent papers about research that was done using Cactus.

8. Cactus is just for Black Hole simulations.

   No. Since Cactus 4.0, Cactus has been a generic framework for any application area. Although it is true that most of the publically available modules provide infrastructure for finite difference codes, and that the numerical relativity community remain our largest set of users.

9. Cactus doesn't have periodic boundary conditions.

   It has always had periodic boundary conditions.

10. Cactus doesn't run on a **?** machine.

    Cactus can run on anything with a ANSI C compiler (e.g. Windows, Mac, PlayStation2). You need MPI for parallelisation, and Fortran for many of our numrel thorns.

11. To compile Cactus you need to edit this file, tweak that file, comment out these lines, etc, etc.

    You shouldn't need to do this! Please tell us. We test Cactus on many machines (see the release notes), and on all of these is works almost "out of the box".