IIRC guys from elementary OS use Inkscape for mockups. There is also Pencil.
Both are free software.
- [Trisquel-users] FSF compliant UI mockup/sketch tool oshirowanen
- Re: [Trisquel-users] FSF compliant UI mockup/sketch tool rakyi
- Re: [Trisquel-users] FSF compliant UI mockup/sketch tool jbar
- [Trisquel-users] Re : FSF compliant UI mockup/sketch tool calinou
