Project IceStorm provides the first end-to-end open source FPGA toolchain, was originally presented at 32c3, and only targetted Lattice iCE40 FPGAs. nextpnr is the next big step for open source FPGA tools, providing a retargetable open source FPGA place-and-route tool that will enable open source flows for many different FPGAs from many different vendors.
nextpnr is a retargetable FOSS FPGA place-and-route tool that is replacing arachne-pnr as place-and-route tool in the IceStorm open source iCE40 flow. (I have originally presented IceStorm and arachne-pnr at 32c3.)
nextpnr is retargetable, meaning it can be ported to other FPGA architectures easily, uses timing-driven algorithms, provides a python scripting API, supports complex placement and floorplanning constraints, and has a nice GUI. Python and GUI support are optional, which may be useful when deploying nextpnr on an embedded platform. In short: It is a big step forward for open source FPGA tools, attempting to close the gap to vendor tools in some aspects, and even setting new standards in other aspects.
As of now, iCE40 FPGAs (Project IceStorm) and ECP5 FPGAs (Project Trellis) are supported in nextpnr, but support for more architectures is expected to follow in short order.