Odoo is the world's easiest all-in-one management software. It includes hundreds of business apps:
CRM | e-Commerce | Accounting | Inventory | PoS | Project management | MRP | etc.
check out this link: http://doc.openerp.com/v6.1/contribute/index.html#how-to-contribute-link and you'll find plenty of information on how you can contribute making OpenERP a better product!
Since the answer from Quentin is quite old I decided to add the 'new' wiki. This explains how to report issues, how to handle tracebacks, how to make PR's (and against which version) and info about translations/labels.
You can find all the information at https://github.com/odoo/odoo/wiki/Contributing