, open source, runs on win/linux/machttp://oss.netfarm.it/mplayer-win32.php
for latest win32 binaries...
mplayer -vo gif89a:fps=15:output=test.gif -fixed-vo *.gif
should work for gif files
mplayer mf://*.jpg -vo gif89a:fps=15:output=test.gif
for jpeg, also png should work...
add -vf scale=320:240 or whatever res you want, if you want to change the gif size
mplayer is a media player (and mencoder is a media encoder) which can play all video files .... ever known. also boasts to be the fastest player as well.