Crosswords (or xwords, to use its Sourceforge project name) is a
free, open source implementation of the rules of Scrabble™ for
handhelds. It is currently shipping on Android, with older versions
still available for PocketPC (including Smartphone) and PalmOS.
Some people call Crosswords "Words without Ads" :-)
Crosswords formerly shipped on the Franklin eBookman, but that platform is no longer actively supported and is not