Maximum possible movement in a turn I've read that for any position, there are on average approximately 35 possible moves. But what's the maximum number of possible moves for a position?
After some searching, it seems that this composition is the current record holder. 218 moves; legal position with promotions:

R6R/3Q4/1Q4Q1/4Q3/2Q4Q/Q4Q2/pp1Q4/kBNN1KB1 w - - 0 1


Another version of the position (same number of moves):

3Q4/1Q4Q1/4Q3/2Q4R/Q4Q2/3Q4/1Q4Rp/1K1BBNNk w - - 0 1


Bonus:

79 moves (for black); from actual game between Davis and Panchanathan, source from Tim Krabbe's list of chess records:

4r1k1/p4pp1/2n2n1B/2b5/N6Q/P2q1N2/1r4PP/R4R1K w - - 0 1


99 moves (for white); all pieces on board:

q2Q3r/n6R/kpB1N1K1/p1p1Bppp/1PN3P1/1n1pp1b1/P1PPPP1P/r5Rb w - - 0 1


164 moves (both sides counted); all pieces on board:

R6R/pbpppK2/1B1QNNp1/1p3p1p/P1P3P1/1Pnnq1b1/2kPPPBP/r6r w - - 0 1


324 moves (both sides counted):

1QqQqQq1/r6Q/Q6q/q6Q/B2q4/q6Q/k6K/1qQ1QqRb w - - 0 1


412 moves (both sides counted); a curiosity, illegal position:

QQqQqQqq/q6Q/Q6q/q6Q/Q6q/q6Q/Q6q/QqQqQqQq w - - 0 1


Main source: Guide to Fairy Chess. The book is a bit old, so there might be new record holders, but if that's the case, I was unable to find them.