draw.io - Online diagramming application
IconViewer - Bot Productions's IconViewer utility allows you to view, copy, and save the icons in a file through its property sheet.
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.
IconsExtract - Extract icons and cursors stored in EXE, DLL, OCX, CPL files
PlantUML - PlantUML is an open-source tool that uses simple textual descriptions to draw UML diagrams.
MailerSend - Better transactional emails for teams.