I say GPL so that you can merge anyone else's improvements (including those by other companies and they make the software publicly available by same license, to

I say GPL so that you can merge anyone else's improvements (including those by other companies and they make the software publicly available by same license, too), you can sell the software with warranty and/or printed documentation and/or DVD with the software on it, and everyone else can do the same. If you do not need this, you can use a simple license instead (such as MIT license)