apache
 apc (for apc_store/apc_fetch)
 apd
 bcmath
 ctype
 curl
 datetime
 domdocument
 hash
 hotprofiler (undocumented FB profiling ext that supports xhprof)
 iconv
 icu
 idn
 image
 ipc
 json
 ldap
 magick
 mailparse
 math
 mb
 mcrypt
 misc
 mysql
 network
 openssl
 oracle
 pdo
 posix
 preg
 process
 reflection
 server
 session
 simplexml
 soap
 socket
 splfile
 sqlite3
 stream
 string
 thrift
 url
 variable
 xml
 xmlwriter
 zlib
Quite a few, but the lack of mysqli, pgsql, and memcache makes it hard to run some apps.