Who wrote the Sefer Besamim Rosh?
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Here's a nice writeup. It was published by R' Saul Berlin, with the claim that only the commentary part was by him, but the core responsa were by the Rosh. Many (maybe most) scholars now believe that R' Saul Berlin wrote both parts and misattributed the responsa to the Rosh.
R' Rakeffet is doing a fascinating lecture series on this work, including a great deal of discussion of why it's now taken to be a literary forgery. You can hear what he's said so far by going here and listening to the lectures marked "Responsa," starting "2010-10-24 Responsa 06." You can also subscribe to an ongoing feed of his lectures (both Responsa and Jewish History, which is equally fascinating) using this RSS link.