Check out this amazing project from John Beetem. Make small Digital Logic designs without the heavyweight vendor tools. Flavia tool chain lets you make bit files for the Papilio One 250K with completely FLOSS software! Only CPLD sized designs are possible, but this is a boon for learning Digital Logic on ARM based boards like the Raspberry Pi.
Abstract: Flavia is a family of logic arrays that can be designed and programmed entirely using free-as-in-freedom (FaiF) software. This is in contrast to standard FPGA (Field-Programmable Gate Array) tools from vendors such as Xilinx, Altera, Lattice, Cypress, and MicroSemi (formerly Actel) where you must use the vendor’s software to design the FPGA. Except for a part from Atmel that never caught on, the author is not aware of any commercial FPGA or CPLD (Complex Programmable Logic Device) that can be designed without running its vendor’s tools.