When I returned to the DM's seat 11 years ago, I wanted to use a familiar system. So, I used AD&D 1e, but with the OSRIC rulebook, which is simply a much easier-to-reference version of 1e. I also purchased a number of Advanced Adventures from Expeditious Retreat Press, and I was very pleased with the content I received from Mr. Browning and Company. A few years later, I was able to snag the first score or so in hardcover collections. Seriously, good stuff.
For just US$9.95 you get all twelve titles in our Starter Collection (retail value $70) as DRM-free ebooks, including the first ten AA modules – from #01: The Pod-Caverns of the Sinister Shroom through #10: The Lost Keys of Solitude – and we add the 2009 bestiary Malevolent and Benign I and the free OSRIC rulebook. For a list of all the modules with links to their sales pages on DriveThruRPG, see the first book entry below, "Advanced Adventures #01-10."
And if you pay more than the threshold price of $35.79, you'll level up and also get our entire Bonus Collection with thirty-four more titles worth an additional $210: all 33 remaining Advanced Adventures modules from #11: The Conqueror Worm through #43 The Warrens of Zagash, and hitting many highlights of the AA line including #15: Stonesky Delve, #23: Down the Shadowvein and #24: The Mouth of the Shadowvein, and both White Dragon Run scenarios. (For the list and the DTrpg links, see the fourth book entry below, "Advanced Adventures #11-43.") We also include the 2018 Malevolent and Benign II monster manual.