This is the only tool here that needs no hosting from anybody. The others put the widget page on a server and pack your content into a link; this one gives you a block of HTML and CSS that is the whole thing. Paste it into a pathway activity, a SharePoint page or a Canvas page and it works on its own, forever, whether or not any of our servers are still running.
It manages that by using no JavaScript at all. A checkbox that you cannot see holds the open or closed state, and CSS shows the dialog while that checkbox is ticked. The trigger and the close buttons are labels pointing at it.
Every modal you generate gets its own randomly named identity, and every class name inside it carries that name too. That is what stops two modals in the same activity from opening each other — a real problem with the shared class names this tool used to emit, where clicking the first trigger opened every modal on the page at once.
So you can build as many as you like and paste them all into one activity. Just generate each one separately rather than copying the same block twice and editing the text, which would give both the same identity.
Being pure CSS has limits worth knowing before you use one for something important:
It is keyboard operable — you can tab to the trigger and press Space — which the earlier version of this tool was not, because it hid the checkbox with display: none and that takes it out of the tab order entirely. For a tip or an aside a modal is fine. For anything a student must read to continue, put the content on the page instead of behind a click.