Mac only: Use this tiny program to find alternate versions of characters in the Unified Han section of the Unicode standard. Some of the results are simplified and traditional versions of characters, while others reflect differences across Asia. The program allows the copy and paste functions, so importing and exporting characters is a snap.
A search for guó 國 yields the following results: 囯囶囻国圀.
龜: 亀龟 醫: 医毉 麼: 么尛庅麽
辯: 弁辡辩 爾: 尒尓尔 絕: 撧絶绝