There is a new alpha version 2.15.2 based on the fork WinMerge jp (source).

One comment here mentions the program hasn't been updated since 2009, but the current version up for download on the product website is from February 2013. So if it was abandoned at some point, it doesn't seem to be anymore.

What I'm concerned about is, as mentioned by another commenter, that it doesn't compare big files and subesequently declares folders as identical that really aren't. Does anyone know whether this is/was a real problem, and whether it might have been fixed since?

Edit: after using the program for a while I suspect the commenter in question might have overlooked the "quick compare limit" setting. It allows to set a filesize limit above which only the first and last parts of a file are actually compared, instead of a thorough comparison. The limit seems to be capped at 2000MB though, so that's something to consider if you want to use it with files larger than that. This only applies to folder comparison, of course. Direct file comparisons are done in full.

no updates since 2009!

I do a lot of binary comparisons to make sure video files and entire CDs/DVDs are exactly the same, bit for bit. WinMerge is a lot slower than Beyond Compare. Otherwise, it works great. It isn't slow enough to make me want to pay for Beyond Compare YET, although I have been tempted.

Technically it works but Beyond Compare is better. Winmerge is free, but it hasn't been updated in ages. Beyond Compare has been under constant development, and it is apparent. Beyond Compare is very polished, and easy to use. Most things it does correctly right out of the box, though it's still worth looking at the menus to figure out what it's doing and not doing.

Winmerge, on the other hand, does things wrong. Once you dig through all the menus and options, you can set it up to do what you want, and it'll do a good job of it, but it's clunky and harder to see the useful information. Beyond Compare is so much better, I'd skip Winmerge even though it's free.

Beyond Compare is not free, but it has a fully-functional 30 day trial, so just use that if you only need it temporarily. If you need it longer, it's worth buying. It's really incredible.

Not impressed with WinMerge. It has problems with refreshing the view, displays pathnames in separate directory/filename columns making it very difficult to read especially in tree mode, doesn't respect the option to ignore CR/LF differences, and various other faults.

I think the best stand-alone compare tool for Windows. Never found another so good.

Great program. I dont care for the default coloring of changed/deleted stuff. I could change it but its just not worth the hassle, I have too many copies of this on other computers to bother.

Doesn't seem to support 3-way file comparison, like Meld and Kiff3.

I've used this tool previously and it is indeed a fantastic tool.