Gcal is a program to calculate and print calendars on the command-line. Calendars can be printed in 1-month, 3-month or whole-year views. In addition, eternal holiday lists can be generated for many countries, which can be complemented by user-made lists of fixed dates to make an agenda. Gcal can also calculate astronomical data, such as the phases of the moon, and supports alternative calendar formats: Julian, Gregorian, Islamic, Chinese and more.

Libical is an implementation of the iCalendar protocols and protocol data units.

ConfClerk is an application written in Qt, which makes conference schedules available offline. It displays the conference schedule from various views, support searches on various items (speaker, speech topic, location, etc.) and enables you to select favorite events and create your own schedule.

At the moment ConfClerk is able to import schedules in XML format created by the PentaBarf conference management system (or frab) used by e.g. FOSDEM, DebConf, FrOSCon, Grazer LinuxTage, and the CCC congresses.

ConfClerk is targeted at mobile devices but works on any system running Qt.

ddate displays the Discordian date and holidays of a given date. The Discordian calendar was made popular by the "Illuminatus!" trilogy by Robert Shea and Robert Anton Wilson.

LibHdate is a small library for the Hebrew calendar and times of day, written in C, and including bindings for C++, pascal, perl, php, python, and ruby. It includes two illustrative command-line programs, hcal and hdate, and some snippets and scripts written in the binding languages.

By default, date2name gets the modification time of matching files and directories and adds a datestamp in standard ISO 8601+ format YYYY-MM-DD at the beginning of the file or directory name.

Date is a header only C++ library that extends the chrono date algorithms library for calendar dates and durations. It also provides the <tz.h> library for handling time zones and leap seconds.

gsimplecal is a lightweight calendar application written in C++ using GTK. Launched once, it pops up a small calendar applet, launched again it closes the running instance. It can additionally be configured to show the current time in different timezones.

Remind allows you to remind yourself of upcoming events and appointments. Each reminder or alarm can consist of a message sent to standard output, or a program to be executed. It also features: sophisticated date calculation, moon phases, sunrise/sunset, Hebrew calendar, alarms, PostScript output and proper handling of holidays.

Hebcal is a program for converting between Hebrew and Gregorian dates, and generating lists of Jewish holidays for a given year. Shabbat, holiday candle lighting, and havdalah times are approximated using your location.

It can also show daily prayer times, the weekly Torah reading, and the daily leaf of Talmud. The program can help with counting of the Omer or with calculation of Hebrew yahrzeits, birthdays, or anniversaries.

Ccache is a compiler cache. It speeds up recompilation by caching previous compilations and detecting when the same compilation is being done again. Supported languages are C, C++, Objective-C and Objective-C++.

The GNU Compact Disc Input and Control Library (libcdio) is a library for CD-ROM and CD image file access. It allows the developer to add CD access to an application without having to worry about the OS- and device-dependent properties of CD-ROM or the specific details of CD image formats. It includes pycdio, a Python interface to libcdio, and libcdio-paranoia, a library providing jitter-free and error-free audio extraction from CDs.

cd-discid is a command-line tool to retrieve CDDB discid information from an audio CD.

GNU ccd2cue is a preprocessor for CD burning software that allows the conversion of the proprietary CCD format to the CUE format, which is well-supported by free software. These files are commonly distributed with CD images and are used to describe how tracks are laid out on the image.

cdrecord converts a CD image in a ".bin / .cue" format (sometimes ".raw / .cue") to a set of .iso and .cdr tracks.

DVDStyler is a DVD authoring application which allows users to burn video files in many formats to DVD discs, complete with individually designed menus. It can be used to create professional-looking DVD's with custom buttons, backgrounds and animations, from within a user-friendly graphical interface.

cdrdao records audio or data CDs in disk-at-once (DAO) mode, based on a textual description of the contents. This mode writes the complete disc – lead-in, one or more tracks, and lead-out – in a single step and is commonly used with audio CDs. cdrdao can also handle the bin/cue format, commonly used for VCDs or disks with subchannel data.

Optical media (CD,DVD,BD) keep their data only for a finite time (typically for many years). After that time, data loss develops slowly with read errors growing from the outer media region towards the inside.

Dvdisaster stores data on CD/DVD/BD (supported media) in a way that it is fully recoverable even after some read errors have developed. This enables you to rescue the complete data to a new medium.

Data loss is prevented by using error correcting codes. Error correction data is either added to the medium or kept in separate error correction files. Dvdisaster works at the image level so that the recovery does not depend on the file system of the medium. The maximum error correction capacity is user-selectable.

CDemu is a software suite designed to emulate an optical drive and disc (including CD-ROMs and DVD-ROMs).

geteltorito can extract the initial/default boot image from CDs (and ISOs) that follow the El Torito specification for bootable CD-ROMs.

Image data is written to standard output by default and all other information is written to standard error.

Asunder is a graphical audio CD ripper and encoder. It can save audio tracks as WAV, MP3, Ogg Vorbis, FLAC, Opus, Wavpack, and Musepack. It can use CDDB to name and tag each track automatically, and it allows for each track to be by a different artist. Asunder can encode to multiple formats in one session, and it can create M3U playlists.

abcde is a front-end command-line utility (actually, a shell script) that grabs tracks off a CD, encodes them to Ogg/Vorbis, MP3, FLAC, Ogg/Speex and/or MPP/MP+ (Musepack) format, and tags them, all in one go.

cdrtools is a collection of command line utilities to create CD's, DVD's or Blue Ray discs. The most important components are cdrecord, a burning program, cdda2wav, a CD audio ripper which uses libparanoia, and mkisofs, which can create various disc images.

Libisofs creates ISO 9660 (also known as ECMA-119) file system images which can either be written to POSIX file objects or handed over to libburn for being written directly to optical media. It can read metadata of ISO 9660 filesystems, manipulate them, and use them to produce new complete file system images or add-on images to be appended to the read file system image. Supported extensions to ISO 9660 are Rock Ridge, Joliet, AAIP, zisofs.