I just finished my call this afternoon and was accepted to the Williams REU for Geometry just now! Other groups are on completely different schedules I'm pretty sure. It's done individually by the faculty mentors, and I don't even know the way the Geometry group is accepting people so don't get worried if you haven't heard back yet!
I normally am not one to post success stories, as I like to stay humble, but I'm posting this here just to let you guys know, that without this community, I would not be where I am today. Idk how many people here know me, but when I first started posting here I was a business school student disillusioned about my motivations in life. I had always liked mathematics throughout high school and was motivated to start again as a sophomore after realizing how empty I felt doing finance work (I was actually initially interested in "physics." One of the typical kids interested in physics from popular science books. Y'all got me out of that phase. Dabbling in proofs and open courseware made me realize that math was really what I wanted to do).
I started taking huge math courseloads every semester, as well as more courses over the summer, and independent studies with professors. All of my course choices, self studying, etc. were guided by this community, especially mathwonk, who gave me a lot of very personal advice (thank you for putting up with all of my annoying PMs). I had read through the whole "who wants to be a mathematician thread," and it was only after learning from your experiences that I was able to figure out how to best position myself for an REU this summer. This was my top choice in REUs and I have already sent Dr. Morgan an acceptance. Thank you all so much for helping me get here. I really was clueless about mathematics before finding this forum, and I wish I was capable of expressing over the internet just how sincere this thank you is. You guys have changed my life.
DH
P.S. For future applicants: I think one thing my situation really makes clear is the importance of good letters of recommendation. I come from a school not known that much for math but pushed really hard to do as much as I could in math, and so the professors I got close with at my school really pushed for me (one wrote tailored letters of recommendation for different programs). I think this ended up helping my application more than anything.