Silice itself (the compiler and its documentation) is licensed under the GPL v3 Open Source license, see full text here. A few exceptions apply when external code under a more permissive license has been included. Each source file contains its license info (if that is missing, please let me know and I'll include it asap).
Example projects are licensed under the MIT license, see full text here. Each example source file contains its license and author info.
The Silice compiler generates Verilog code, that can then be fed into an FPGA toolchain. Beyond your own compiled code, this Verilog code embeds some Silice specific glue code. This glue code is entirely under the MIT license, so that you can freely use Verilog code compiled with Silice from your own source files.
Silice depends on a number of external libraries. These are included in separate directories with their own license files.