> Where is it possible to find the list of Trisquel software that > comes by default like i.e. LibreOffice?
Most graphical applications will appear under Add/Remove Applications, with some exceptions. If an application does not appear there, search for it in Synaptic Package Manager. Synaptic displays everything in the repository, so it is more complete than Add/Remove Applications but is harder to navigate because in addition to applications like LibreOffice it contains other packages like libraries. You can also search the repository from a terminal via $ apt-cache search [list of substrings to filter by]
