From publisher blurb:
The warlock has made a pact with a powerful extraplanar being, gaining magical powers and spellcasting ability.
This is a conversion of the 5th Edition warlock to OSR systems, most notably first advanced edition, but also the original rules and and the basic/expert (B/X) sets.
(Previously I had created a class named the warlock, but based on a third party intrepreation of the third edition class and is quite different than this, as the 5th edition rules did not yet have an SRD and that warlock was not open content. I tried to stick as close to the 5th edition class as possible, making some minor changes to fit the older system better based on playtesting, as well as filling in gaps because the SRD5 is kind of sketchy. For instance, I added several new patrons to its one, and a handful of new invocations that suggested themselves in play.)