ACM has made 'Concurrency: the Works of Leslie Lamport' free to download
Wow, nice move. I suggest anyone who considers themselves to be serious about distributed systems or operating systems take advantage of this opportunity. Leslie was hugely impactful on my early career at Sun where I ended up being the "ONC/RPC architect." One of the people who whose work I admired was Andy Birrell (who many will agree "invented" of RPC). It felt that every time I reached out to Andy on a problem that seemed complex and untenable, he would point me at one of Leslie's papers.