Las extensiones (librerías) disponibles en PHP 5.1 en servidores con selector de versiones son:
| bcmath | gnupg | lzf | pdo_pgsql | sybase_ct | |||||
| big_int | haru | mbstring | pdo_sqlite | sysvmsg | |||||
| bitset | huffman | mcrypt | pgsql | sysvsem | |||||
| bz2_filter | idn | memcache | quickhash | sysvshm | |||||
| coin_acceptor | igbinary | msgpack | radius | tidy | |||||
| crack | imagick | mysql | redis | timezonedb | |||||
| dba | imap | mysqli | snmp | translit | |||||
| dbase | inclued | ncurses | soap | xdebug | |||||
| dom | inotify | odbc | sockets | xmlreader | |||||
| doublemetaphone | interbase | pdo | sourceguardian | xmlrpc | |||||
| gd | ioncube_loader | pdo_firebird | ssh2 | xmlwriter | |||||
| geoip | ioncube_loader_4 | pdo_mysql | stats | xsl | |||||
| gmagick | ldap | pdo_odbc | stem |
