Learn German: Welche Software installiert sich schneller?

This is a passive alternative. By using the reflexive pronoun sich, the sentence expresses a passive idea—the software is being installed by someone—without using werden. German often uses this reflexive construction to describe how an action affects the subject, especially with adverbs of manner like schneller, gut, or leicht (e.g., Das Buch liest sich gut).

Why is the ending on Welche an -e?

Software is feminine in German (die Software), so the interrogative word welcher takes the feminine nominative ending -e to become Welche. Loanwords from English often take the gender of their direct German equivalent (the German word for ware is die Ware).

Since schneller means faster, why doesn't it need an adjective ending here?

In this sentence, schneller is acting as an adverb modifying the verb installiert, not as an adjective modifying a noun. Adverbs in German do not take declension endings, even when they are in the comparative form. If it were modifying the noun directly, it would need an ending, like eine schnellere Software.

Can I use this reflexive trick to turn any passive sentence into an active one?