Many functionality is offered by a number of builtin modules, as Math, for mathematics functions, or Marshal, to transform complex objects into a single string. Some builtin modules are listed in the following table
| Name | Content |
|---|---|
| Kernel | Implements main methods and statements |
| Comparable | Methods for comparisons |
| Enumerable | A lot of iterators |
| Marshal | Data serialization |
| Math | Mathematical functions |
| Process | System process management |
| Signal | System signal processing |
What is not implemented into the languages or the builtin modules is into a standard library, structured into modules and distributed along with the language; there are about hundred modules in the standard library, in the following table a list of some modules.
| CGI | Common gateway interface |
| CSV | for CSV files |
| Curses | To deal with textual interfaces |
| Digest | compute digests |
| erb | html template (used also by rails) |
| find | the unix find utility |
| gserver | for tcp net servers |
| ipaddr | for tcp/ip addresses |
| json | json parser and writer |
| logger | messages to the system |
| matrix | vector and matrixes in Ruby |
| net/ftp | ftp client |
| net/http | httpd client |
| net/imap | imap client |
| net/pop | pop client |
| net/smtp | to send mail |
| net/telnet | remote connection |
| socket | socket implementation |
| openssl | ssl sockets connection |
| rss | parse rss streams |
| scanf | the scanf function of the C language |
| set | for the set algebra |
| shellwords | split a phrase in an array of words |
| singleton | makes a class with a single instance |
| socket | BSD sockets for network applications |
| syslog | writes on the system syslog |
| tempfile | temporary files management |
| tk | interface to the tk language |
| webrick | http server |
| xmlrpc | xmlrpc implementation |
| yaml | yaml parser and serializer |
| zlib | for file compression |
| marshal | to serialize using binary files |
| gems | virtual environments and gems management |