Open Education Handbook/Open Source Education Tools
Open source software is software where the source code is openly licensed so others can change and distribute the software to anyone and for any purpose.
Naturally the open community are keen to support open tools and there are a significant number of open source open education tools available.
There is a considerable amount of open source software for use in the education sector. An impressive list is available from OSSWatch.
The Free Software Foundation Europe(FSDE) also write a blog and have a section on education