I'd like to compile a list of all the computer programs out there that people can use for learning/reading seforim with. There are many of them now a days (and perhaps were some in the past that are no longer being supported.) However I'd like to keep a list to what is currently being supported and used now a days. It can be software or apps used on any or all of the following platforms: Windows, Mac, iOS (iPhone and iPad), Android, Blackberry, Internet-based (anything viewed or accessed through a web-browser). And whatever other platforms there might be out there right now running current seforim software.
Wikipedia has an extensive list of the Torah database software programs currently available.
Any PDF (e.g. from HebrewBooks.org) opened in Safari on the iPhone can be saved to the program iBooks and read even when not connected to the Internet. Likewise, on any non-mobile computer, it can be saved to the hard drive and read later in Adobe Acrobat Reader. Free to use.
The Bar-Ilan Responsa Project is a project being compiled by Bar Ilan University which has typed-up versions (not PDFs, just the text) of many seforim, ranging from Tanach and Shas to hard to find responsa seforim, it is available in an online version, a CD version and a USB version, and can be accessed on smartphones. Subscription required for full access, but has free limited searching.
Otzar HaHochma is an online resource with OCR'd PDFs of many books, including some that are not included in Bar Ilan (such as the Da'at Mikra series). Also available as a Windows program. Subscription required for full access, but first 40 pages of each sefer are available for free, as well as limited searching.
TES Jewish Software has many PC and mobile programs available for purchase and download. Examples include the Artscroll Stone Chumash CD-ROM, Holocaust Responsa Project, and Encyclopedia Judaica. (Link to Downloads)
Halakhah.com is an online resource with the Soncino English translation of the Talmud. Free to use.
The Mercava is an interactive website with tzuras haDaf, translations, and commentary. Free to use.
DafYomi.co.il is a website with PDFs, translations, commentaries, and summaries of the Talmud. Free to use.
Chabad.org has a database of many seforim in English and Hebrew, such as Tanach with Rashi, most of the Mishneh Torah in English with notes, many Lubavitch seforim, among others. Free to use.
Sichos In English has many of their books typed up online, which include translations of Lubavitch Seforim as well as many essays on Chassidus and other topics. Free to use.
Otzar 770 has most of the talks of the Lubavitcher Rebbe, R' Menachem Mendel Schneersohn hyperlinked and in picture format. Free to use.
Munkatch Seforim has most of the seforim of the Chasidic dynasty of Munkatch available for free download as PDFs.
Torat Emet is a free software alternative to the Bar-Ilan Responsa. It has typed up versions of many sefarim (from Tanach up to some works of Rav Ovadiah Iosef). An online version of the site is available, as well as an older version of the site.
Sefaria.org is a free to use website with a continuously growing collection of Hebrew texts and crowd sourced translations. It also has a tool for easily making beautiful source sheets.
Mishna Berurah Online in Hebrew. Cut and paste-able text for Shulchan Aruch and Mishna Berura. The letters in parentheses will bring you to the text of the Mishna Berurah and the asterisks will bring you to the Biur Halacha.