Whimsical Wireframes - Lightning fast wireframing with real-time collaboration.
Zeplin - Collaboration app for UI designers & frontend developers
Userflows - Automatically generate user journeys
avocode - Centralize design collaboration, version control, prototyping, feedback, and developer hand-off with Avocode. Work on any design, anywhere, with anyone. Sign up free 👉 https://avocode.com/.
Adobe XD - Adobe XD is an all-in-one UX/UI solution for designing websites, mobile apps and more.
Mockplus iDoc - Handoff designs with accurate specs, assets, code snippets