Lots of them - and they aren't necessarily free
Open source licences... much of a muchness?
Indeed. Let me start by saying, if you happen to think that all open source software is created equal, you are very, very wrong.
'Open source licence' is a very general term which refers to a software licence that allows the licensee to change or distribute the source code to some degree without paying the person who created that software.
Sounds pretty simple.
Well that's where the simplicity ends.
There are many, many different types of open source software out there - it's a jungle, really. Some are created by vendors, some by independent groups. You may have heard of some of the more common ones such as the GNU GPL (General Public Licence), BSD licence or Mozilla public licences. But this is just the tip of the proverbial iceberg.
I'm feeling cold.
The Open Source Initiative (OSI), a not-for-profit organisation which spends a lot of time thinking about the question 'what is open source?', has approved around 30 different open source licences. This means the OSI believes these licences fulfil its definition of open source and any software using them can call itself 'OSI Certified Open Source Software'. You can see the OSI's definition here or the OSI's list of approved licences here.
But that's just one definition and there are more beyond those OSI-approved licences which some consider open source as well.
Still... I'll know it's open source because it's free, right?
Not so fast - open source is not the same as free! The Free Software Foundation (FSF), for instance, has its own criteria for what should be considered 'free software' - and it's not necessarily the same as open source. You can read more about the FSF view here.
That said, you should realise that you may well end up paying for open source software - if not through licence fees then through service and support fees, for instance.
Anything else I should know?
Well there is this thing called dual licensing
Oh boy... please explain.
Software makers can release their products under more than one licence - usually for different types of users. So home users get it free and business users have to pay. That sort of thing. One example of dual licensed software is the popular MySQL database.
OK... what else?
Then there's shared source - an idea Microsoft is keen on which gives users access to limited amounts of the source code without paying the company but does not allow for reuse of the code for commercial purposes. It's not technically a licence, though, just a programme run by Microsoft and some other vendors as well.
I think I get the basics. But what's the most important thing for businesses to know about OS licences?
Open source does not mean one thing. There is some general consensus around the definition but, as you can see from the literally dozens of licences out there, one product called 'open source' could have quite different legal stipulations for use to another.
When using open source in an enterprise, find out which licence the software is released under, and whether or not it's a dual licence, and then do your homework (or hire a lawyer) to make sure you know just what you're getting into.