Form Tools 3 is a complete rewrite of the Form Tools code, adding in PHP 7 support (among other things). Over time, the alpha package will be updated to include all the components available in the main build.
Good question! You may see checksums from time to time wherever there's downloadable content. They're there for developers to confirm that the file being downloaded hasn't been modified in any way and contains only the code that the original developers intended. By and large you don't have to worry about it, but the info is there if you need it.