I just discovered a great free tool: a virtual white / #blackboard for hand-drawn #diagrams. Browser-based, with options for #selfhosting and building into your own app. Supports #collaboration and end-to-end encryption (for generating share links). Also easy to export file or save as an image.
Fosstodon is an English speaking Mastodon instance that is open to anyone who is interested in technology; particularly free & open source software.