Commercial Open Source
I really like the term, “Commercial Open Source”. It is Open Source and/or free of charge if you use the lite or standard version. In most cases for small businesses or when you want to use it for your one no big deal. When your company is growing and you need more features or users, the vendor is going to charge. Is there a way back? Proberly not, your little system contains to much information and your users have gone familair with the tools.
Good exampes are, Suger CRM, YesHello, some Google Apps, Hyperic, etc.
By using these kind of sales models, you may be certain that they use the revenue for some kind of R&D and hopefully the vendor grows, where you as an user may feel the benefits.