Sort of old news, I guess, but worth saying: this is one of the 3 most-used tools at Matasano. It's a really excellent piece of code.
The thing that sets Burp apart from (say) Tamper Data in Firefox is the fuzzer (Burp calls it the "intruder"). The free OWASP WebScarab also has a fuzzer, but it's not as good.
Is an Intel-only version and an update of the website in the plans somewhere?
I also want to know what the two other apps are :)
Unix, works well, has some of the nicest apps out there is my guess.
(I split most of my work between my Mac and Linux)