Open Source for Enterprise Management?

acooks asks: "After a recent talk on Open Source software to a class of MBA students, someone came to me with a huge opportunity to use Open Source to manage business processes. What they want is SAP, but for small to medium sized businesses and at a price that a small business can actually afford. Furthermore, they realised that Open Source isn't going to go away anytime soon and that they might as well try to use it to save costs (If IBM is embracing Linux and SAP & IBM plays nicely, then maybe it's worth finding out more about Linux). The questions that were raised basically boils down to this: Is there Open Source software available to manage a business or some of the business processes? Where do you start looking for something like this? I realised that this isn't something that you can quickly download from SourceForge or Freshmeat, so now I'm asking Slashdot."