OSRIC, Old School Reference and Index Compilation. Basically, this is AD&D 1E under the Open Gaming License.
Many people, including the author of the OSRIC book, will tell you that OSRIC is nothing more than a platform on which new resources can be made available that are compatible with AD&D 1E.
Since it's introduction and gain in awareness, many people have commented that for new people learning AD&D 1E or even for people who are coming back to the game but don't have the core books, etc.. that OSRIC is the better way to go in terms of introduction.
OSRIC is easier to understand, they say. The rules are made clearer and more obvious. With certain small and brief deviations from the original material, I would have to say I agree with those comments.
If one were to gauge players of AD&D 1E by placing true "By The Book" folks at one end and total "Homebrew" people who see the core books at most as general suggestions but nothing to take too seriously, then OSRIC falls in the middle, on the BtB side of the middle line.
That's OK though. The goal of the book/system is to make the game as similar as legally possible to the original AD&D core books. It wants to keep it close to the original where ever possible.
At the same time, it's obvious that they want to make the game as accessible as possible to as many players as possible and chose to "tidy up" some of the areas that perhaps they felt needed tidying up the most.
Even as a DM I find myself referring to OSRIC more frequently in making certain determinations and trying to acquaint myself with a less used rule.
I am probably as close to a total Homebrew DM as one can get. I love having the core books but I have no problem houseruling where I see I want things to be.
Having said that, even being a notorious homebrewer, it's good to have some base point. Something to start with and, if need be, tweak from there.
OSRIC is very good for the homebrewer I find.
I own the main core books of AD&D 1E. The Players Handbook, The Dungeon Masters Guide, Monster Manual and Monster Manual 2. The rest I have no personal use for.
I use my core AD&D books a lot. Especially as I don't use published modules but write every one of the games in my campaign. The books become even more valuable to a homebrewer, in my opinion, than they are to those who mostly stick to published modules.
OSRIC fits into my homebrewing even more because I have it in PDF and easily accessible on my computer. I don't always have my AD&D core books with me, but I have my OSRIC PDF in a remote directory which means that as long as I have my laptop (which I usually do) and as long as I have a wifi connection (which is pretty common these days), then I have access to OSRIC which has kept me engaged in many a spare moment away from the house.