Who knows about skiros package?

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Does anyone know why it is not in the Github repository of ROS?

What would be "the Github repository of ROS"? There are many different Github organisations across which there are even more repositories containing multiple ROS packages. There is no single repository.

The package you mention is probably: frovida/skiros. That is a community contributed package and as is typically the case, those are found in repositories on personal or organisational Github accounts.