Write SQL against a real chemical database and read the rows back, with the structures drawn. The database runs in the page, so a query that would take a server down takes only your own tab.
The same data can be searched by substructure, browsed table by table, or worked through as a tutorial and a set of marked exercises.
Ask the same question of a chemical dataset in SQL and in Mango and compare the two answers. The database is a SQLite file your browser downloads once and queries locally, so nothing you write ever leaves your machine — which is also why the tool needs JavaScript.