All three genders have some plural endings with -s. However, this type of ending is mainly used for words imported from foreign languages, in abbreviations and names:

das Hotel → die Hotels
der PC → die PCs
Herr und Frau Schmidt → die Schmidts

Foreign nouns which don’t add an -s in the plural include: der Manager → die Manager, der Computer → die Computer. Also note that words from the English which end in ‘-y’ have the German plural form -ys: die Party → die Partys.

Nouns from Greek and Latin

A number of words imported from Greek or Latin have the following plural patterns:
• nouns ending in -us or -um change its ending to -en in the plural:
der Organismus → die Organismen
das Museum → die Museen

• most nouns which end in -ma replace this form with -men:
die Firma → die Firmen
das Thema → die Themen