The UQLab software is split into a content management system (UQLabCore) which is closed source and subjected to licensing, and a set of scientific modules (simply called UQLabModules) which are available open source.
UQLabModules is not a standalone software.
To function properly as an uncertainty quantification framework, UQLab requires both the UQLabCore and UQLabModules. That is, UQLabModules makes use of the advanced API provided by UQLabCore to function properly.
Why the licensing system?
The co-founder of the UQLab project explains the reasoning behind this licensing in his blog post.