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Well, you basically just described Basecamp but you need something like FreshBooks - http://www.freshbooks.com/ - for the invoicing part. Nothing I know of that does both parts though. EDIT: Maybe you try something you host yourself with a wiki software or something like - http://www.activecollab.com/ - or - http://collab.ws/. Basecamp alternatives - https://company.podio.com/ - http://www.zoho.com/projects/ - http://lighthouseapp.com/ - http://goplanapp.com/

Thanks!