Open-Access Text Repositories
AlHaTorah.org — I’m a big fan of this always-growing and fully open-access repository of classical texts, and, notably, artworks. The reading interface for the Hebrew texts is highly customizable and easy to read both on mobile and web. It’s edited by rabbis and scholars knowledgeable in the textual witnesses (the manuscripts upon which our printed texts are based). The website started as a Mikraot Gedolot, featuring the classic Torah commentaries, and it’s expanded to include not just Shas but also a wealth of other texts of the Rishonim. It has both English and Hebrew interfaces.
Daat — A Hebrew-only text repository that is reliable, functional, and includes texts that are hard to find elsewhere. One of the best features of Daat is its (low-tech) text formatting, in which paragraphing and colors are utilized to make classical texts easy to parse. Daat has been around since the early days of the internet (and looks it) but it’s a great resource and not to be overlooked.
HebrewBooks.org — An astoundingly comprehensive resource, despite its low-res and sometimes off-kilter or incomplete scans. HebrewBooks does require some informed browsing, in the sense that it throws all possible results at you and you have to know something about the printing history of the text to know which edition is worth looking at.
Sefaria — Although it’s a wonderful concept that I fully support in theory, I can’t wholeheartedly recommend Sefaria. There are no scholars or rabbis working on the texts or translations; they’re extremely uneven in quality and therefore unreliable. I do use Sefaria for quick look-ups and cross referencing, but not more than that without checking against a reliable text.
Paid-Access Text Repositories
Bar Ilan Responsa Database — The gold standard of text repositories, Bar Ilan encompasses far more than just responsa: it’s the whole Jewish bookshelf digitized from standard texts and some manuscripts, all made searchable and clickable. For that, you’ll have to find an access point at an institution that subscribes, or pay for a subscription. (Heads up, even if you have remote access through an institution, Bar Ilan is notoriously cranky about proxy servers and I’ve never been able to connect from home.) There are different subscriptions tiers, and none of them are cheap, though certainly worthwhile if they’re in your budget. Its English-facing site is nominal.
Otzar haChochma — Also great, Otzar has a different approach to text search and display: it shows you the actual tzurat ha-daf of all the works in its (vast) collection. You can search by publisher (e.g. Machon Yerushalayim, Mosad haRav Kook) and inside the texts, and seeing the results is just like opening up the sefer. The downside is that the texts are not as interlinked and readily cut-and-pasted as in Bar Ilan. Bar Ilan is easier to use, but Otzar is arguable more pleasantly readable. And, though it also comes with a not-so-small price tag, Otzar is more affordable. Also, there’s a well-known way (an ethical one) to gaining access to the database through the Spertus Institute, which is an institutional subscriber. For a donation of USD50 per year, you get a “SpertusWeb” membership, which includes remote login access to Otzar. Here is how to subscribe through Spertus. Like Bar Ilan, it’s basically an all Hebrew interface.