A little while ago I was contacted about a new merge tool from the company behind PlasticSCM. (I haven't used Plastic myself, but I'd heard of it.) My initial reaction was that I wasn't interested in anything which required me to learn yet another source control system, but SemanticMerge is independent of PlasticSCM.
My interested was piqued when I learned that SemanticMerge is actually built on Roslyn. I don't generally care much about implementation details, but I'm looking out for uses of Roslyn outside Microsoft, partly to see if I can gain any inspiration for using it myself. Between the name and the implementation detail, it should be fairly obvious that this is a tool which understands changes in C# source code rather better than a plain text diff.
I've had SemanticMerge installed on one of my laptops for a month or so now. Unfortunately it's getting pretty light use – my main coding outside work is on Noda Time, and as I perform the vast majority of the commits, the only time I really need to perform merges is when I've forgotten to push a commit from one machine before switching to another. I've used it for diffs though, and it seems to be doing the right thing there – showing which members have been added, moved, changed etc.
I don't believe it can currently support multi-file changes – for example, spotting that a lot of changes are all due to a rename operation – but even if it doesn't right now, I suspect that may be worked on in the future. And of course, the merge functionality is the main point.
SemanticMerge is now in beta, so pop over to the web site and give it a try.