Siemens clearly believes that designers will choose Solid Edge for their CAD needs if given the opportunity to do a bit more than just download and play with the software. This free download is a serious commitment from Siemens to make much more than the software available to designers.
First, it is a 45 day trial so you have more than 6 weeks of time to work with Solid Edge. Second, you have access to training materials and videos online. Third, you can participate in the Solid Edge newsgroup to gain valuable insights into the program and learn more rapidly from the experience of other users.
Last but not least, Siemens has made Solid Edge available on a monthly subscription which makes it simple and affordable to transition your projects to the Solid Edge design environment.
If you are looking for free 2D mechanical CAD tools, download the free Solid Edge 2D Drafting program. It's not a trial version, but a free, full, production-quality 2D CAD tool.