The Small Catechism of Saint Peter Canisius is one of the best small catechisms. It contains important truths, some of which must be known by necessity of means in order to be saved, that is, truths so essential that even invincible ignorance cannot excuse one from knowing them.
Pope Benedict XIV, Cum religiosi, chap. 4: “See to it that each parish priest fulfills what is prescribed for him by the holy Council of Trent and by your synods: that Christian doctrine is taught, on designated days, by the schoolmasters and schoolmistresses; that confessors fulfill their duty when someone presents themselves at their tribunal in ignorance of what must be known by necessity of means (necessitate medii) in order to be saved…” (source: vatican.va)
The current text is a translation of the following French version:
Gustave De Lamarzelle. (1861). Catéchisme du vénérable père Pierre Canisius de la Compagnie de Jésus. Traduction française. Vannes. Imprimerie Gustave De Lamarzelle. Download here.
The seven volumes of Saint Peter Canisius’ Great Catechism can be found in French for download here.