  We present new, and mostly sharp, bounds on the maximum length of certain
generalizations of Davenport-Schinzel sequences. Among the results are sharp
bounds on order-$s$ {\em double DS} sequences, for all $s$, sharp bounds on
sequences avoiding {\em catenated permutations} (aka formation free sequences),
and new lower bounds on sequences avoiding {\em zig-zagging} patterns.
