We are about to start developing an ERP for small companies, and the question is if there is some free framework for ERP that I can use? Is something done to accelerate the process?
It's a little unclear from your question what you're wanting. If you want to use existing open source ERP software and possibly extend it (subject to the terms of its license), there's a nice list at List of ERP software packages on Wikipedia.
If you're wanting a framework that will help you write a custom ERP package, I am not aware of any such software. I'd treat it like any other software project - gather requirements, then look for pieces that can be used off-the-shelf. Some examples:
And so on. Don't go overboard; use only the pieces you need.
EDIT: Apparently at least one ERP framework exists: WyattERP. If you're comfortable with Tcl, it may be worth a look.