Most of the apps I use have nothing to do with quilting.
I have 2 drawing programs I use for quilting designs.
Adobe Ideas: pull in a pic of the block and audition quilting designs.
Penultimate: practice small FMQ motifs with your finger
General sketch:
Calc & Draw: Drawing board with calculator. I sketch things out and calculate sizes, number of blocks, yardage etc.
I also have iQuilt, QuiltFab and BlockFab-HD, but have never used them.