Whimsical Wireframes - Lightning fast wireframing with real-time collaboration.
Now UI Kit - A beautiful Bootstrap 4 UI kit. Yours free.
Adobe XD - Adobe XD is an all-in-one UX/UI solution for designing websites, mobile apps and more.
Module 02: Layouts - Professional toolkit for UI/UX design
Userflows - Automatically generate user journeys
ArchitectUI - Modern dashboard template for bootstrap 4