Serial Cloner is a software useful for almost everyone. It can handle sequences, linear or circular, look for restriction digests or ORfs or other. You can trim sequences, calculate Tm and %GC and export the sequences to query databases. Great tool to design and test PCRs, ligation and cloning experiments. The best, its available on Windows and on Mac!
http://serialbasics.free.fr/Serial_Cloner.html