You need a synthesis tool - and there are open source alternatives. You need a cell library - a direct derivative of knowing a bitstream format. You need a place and route tool - as soon as format is known such tools would appear (as it happened with ice40). You need timing analysis, probably the hardest piece for community to produce without having an insider knowledge enjoyed by the vendors.<p>All this stuff, including the libraries, can be pretty compact. There is no justification whatsoever for the ISE and Vivado bloat. The essential tools should be very compact. There are multiple copies of a microblaze toolchain, for example. WTF? I need <i>none</i> exactly. Zero. Nil. Stop bundling all the crap, please! Put it in a separate package so everybody could happily ignore it.