Not only desktop, but most mobile platforms as well. Beeing coded in a single C file makes it portable as hell. Their documentation is also a prime example, with great insight.
A fun trick is to ask a colleague at work how many SQL databases they think are in the room. They almost never bear in mind SQLite is heavily used on phones, not even just smartphones.
Not only desktop and mobile, but it can be used as the storage format for larger scale distribued systems. For example it's the on disk format for FoundationDB.
>Beeing coded in a single C file makes it portable as hell.
It kind of is... the SQLite "amalgamation" process takes all of SQLite's source code (across 100+ files) and concatenates it together into a single sqlite3.c file: https://www.sqlite.org/amalgamation.html