I don't know about favorite, but I liked Chip's Challenge (now on Steam) and Oxyd (cloned as Enigma) as early games.
Journeyman Project trilogy was also pretty good but didn't have a huge following.
I can't think of a contemporary game off hand. I guess many of the indie games I've bought over the years in Steam and Humble Bundle sales.
The open source development model isn't good for single player, story based games. Aside from the fact that one have to spoil the story itself, and all of the secrets to contribute, testing a single player level gets boring after a while, so a lot of developers crank up the difficulty by making it harder, so that it remain challenging for themselves but which makes impossible to complete for newbies.
Good examples are Enigma (clone of an obscure puzzle game) and SuperTux (Mario-clone). The latter has boringly simple level design at the beginning, which suddenly gets frustratingly difficult later, while the former has a lot of puzzles which requires obscure geek knowledge or abusing of engine quirks to solve.
And there are a lot of technical blunders, too. The game Widelands(Settlers2-clone) stores all of its sprites ~~in a single file~~ in separate files (instead of a big data file or sprite-sheet), which not only wastes space on Windows but also make the loading slower.
Edit: correction about sprites.
Try Enigma. It's a puzzle game where you roll a marble (or two or three) around with your mouse to solve puzzles.
The early levels are pretty basic and not all of the puzzles use a ton of memory, but it might do the trick.
If you like, there's also an open-source remake called Enigma. Haven't checked it out yet so I don't know if it has all the original features, but it has thousands of levels it seems.
Much older than the timeframe, but any of the Oxyd games, maybe? There's also a newer open-source clone called Enigma.
Here's its website. It's a puzzle game that I've done a few individual-level speedruns of. (I've also created a few levels for it.)
The basic idea is that you control the movements of a marble around a level full of objects that react to it in different ways. Technically, the victory condition of most levels is to match pairs of blocks of the same colour (e.g. hit red then red, blue then blue, etc.), but in practice, the levels tend to be more about actually finding or reaching the blocks than matching them (although the randomization of the colours can often lead to some interesting routing problems, especially in levels which show you the colours in advance).
The game's a little hard to get into because it's basically just a collection of levels with no framing or linking around them, and the interface for selecting a particular level isn't all that intuitive (although you can do them in any order), so many people end up doing only the easiest levels and getting bored. (OTOH, the hardest levels can be very hard, so I can see why the developers wanted to guide people towards the easier levels first.)
The game as a whole doesn't have a victory condition. "Complete all levels" is probably the closest thing it has, but as far as I know, nobodys actually done that on the most recent version as there are over a thousand levels, some of which take hours.
The game you're looking for is actually called Enigma: Website here: http://www.nongnu.org/enigma/ Nice game that is fun to play but can also be VERY challenging.
But in my case, you had a set amount of mirrors that you could place around the stage via the mouse.
People do IL runs of Enigma, which is a spiritual successor to Oxyd. There are some IL records posted at the bottom of this page (together with some advertising that misses the point of advertising so badly it has to be seen to be believed).
Disclaimer: I've contributed levels to Enigma.
Well, I wanted to preserve some of the Enigma style, and the buttons were as big as a normal tile:
http://www.nongnu.org/enigma/images/screenshots/ral38_1.png
Personally I think you don't need that much precision for a button, either you stand on it or you dont :D But for the main reason to preserve the style
Awesome! I had a good feeling that was probably going to pan out.
Looks like you should be able to find a download for Oxyd easily to plug into DosBox, but if you haven't come across it already, also check out Enigma - It's an open source clone with over 1,000 levels including 161 adapted from the Oxyd games and 91 from Esprit. I've downloaded it and plan to check out what all the fuss is about tonight.