I had some work for FPGA on Windows, but now I want to change the platform to Linux. I am looking for some VHDL IDE instead of Xilinx?
There's a big difference between the IDE (development environment) and the simulator. The IDE might come without a built-in simulator, and the simulator might come without a GUI.
If you're looking for a simulator, here is a list of free VHDL simulators with download links. Most simulators work on Linux too.
Historically, the electro engineers were mostly home in a Windows environment and also used to pay a lot for their working environment. This may constribute to an explanation why we do not see more Open Source IDEs for FPGA development. With the increased capabilities of FPGAs and the trend to run Linux on them, this is of course also affecting the development platforms. So, have many thanks for this question, which help in their very own way to broaden the FPGA Linux user base.
For regular-sized projects, when your code can be reasonably edited with regular text editors, I am tempted to say that Debian/Ubuntu Linux as a whole is already a completely Free (as in speech and beer) integrated development environment: the yosys pipeline was packaged so you truly get from the Verilog source code to a flashed Lattice FPGA, see http://www.debian.org/FPGA/Lattice. There is nascent VHDL frontent to yosys at https://github.com/forflo/yodl which I volunteer to package if I get your help testing it.
On a sidenote, the yosys pipeline works across all archictures of Linux. Especially to note are ARM and all the small devices like the Raspberry Pi.