Envelope is a complete platform that makes building web apps on top of PostgreSQL easy.
For a one page overview visit http://envelope.xyz/
For a slide show summary of how Envelope works visit: http://envelope.xyz/how.html
For a slide show summary of how Envelope compares to other web stacks visit: http://envelope.xyz/advocacy.html
Envelope is released with a PostgreSQL style license. If you can use PostgreSQL in your project, then you can use Envelope. Official License: http://envelope.xyz/license.html
The Envelope team has gone to great pains to provide a free installer for Envelope users. Please visit http://envelope.xyz/download.html to get the latest Envelope installer for your platform.
Linux, Mac OS X and FreeBSD versions are provided and should work for most users. Please submit feedback if your platform is missing or you have any trouble. The installer is maintained by nunzio at envelope.xyz.
If for some reason you need to compile Envelope yourself, manual install instructions are included in the INSTALL file.