Mir - The purpose of Mir is to enable the development of user interfaces shells.
LucidChart - LucidChart is the missing link in online productivity suites. LucidChart allows users to create, collaborate on, and publish attractive flowcharts and other diagrams from a web browser.
Y Window System - Y Window System is a platform that allows you to improve the speed, working, and efficiency of the application in your operating system and helps you to increase the responsiveness of applications similar to any locally based app.
draw.io - Online diagramming application
Wayland - Wayland is intended as a simpler replacement for X, easier to develop and maintain.
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.