Pencil Project
Open Source
Pencil Project is an open-source GUI prototyping tool.
UXPin
Commercial
UXPin is a collaborative design platform, allowing entire teams to participate in the design process from start to finish.
Gravit Designer
Free
Gravit Designer is a cross-platform, free design tool.
Compare Adobe XD with alternatives
Compare Pencil Project and Adobe XD and decide which is most suitable for you.
Compare Gravit Designer and Adobe XD and decide which is most suitable for you.