Quick Flutter apps
These are just two Flutter webapps embedded in this page. It's difficult if not quite impossible to tell them apart from the actual installable mobile apps.
The top one invites people to a non-existent party at my place and allows them to sign in and leave comments. The second one (further below) is really simple.
The point of these is that, with Flutter, you get fully fledged mobile apps (Android and iOS), web apps, mobile web apps, Progressive Web Apps and - if it's simple - Windows and MacOS apps as well. The Windows/MacOS/Linux piece is still very beta, so it's not guaranteed at all....but even getting the rest from one codebase is really cool.
This second one just offers lists of randomly generated names that might be suitable for a startup. You save the ones you like.