These are the most popular functions missing in SQLite:

crypto: cryptographic hashes like MD5 or SHA-256.
fileio: read and write files and catalogs.
fuzzy: fuzzy string matching and phonetics.
ipaddr: IP address manipulation.
json1: JSON functions.
math: math functions.
re: regular expressions.
stats: math statistics — median, percentiles, etc.
text: string functions.
unicode: Unicode support.
uuid: Universally Unique IDentifiers.
vsv: CSV files as virtual tables.

There are precompiled binaries for Windows, Linix and macOS.