The MIT License is a shareware license that is quite wide open.  It reads:


Copyright (c) 2009 J. L. Doty

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.


It basically says you can do whatever you want with the software as long as you keep the above copyright notice and license in tact in the code.

It also says that you agree that if you use it, you bear all liability and responsibility for that use, and the author (me) is absolved of all responsibility.  Basically, if you're foolish enough to use shareware software in a mission-critical application, and because of it your company is driven into bankruptcy, or a lot of people are killed, or any problems arise, you accept the fact that you're the fool that is at fault and liable, not me, the author.