Most of the code here is licensed under the LGPL.  There are exceptions which have their own licenses, listed below.  See comments in those files for more details.  

util/murmur_hash.cc is under the MIT license.  
util/string_piece.hh, util/string_piece.cc, and util/double-conversion are from Google; see the licenses in the code or util/double-conversion/LICENSE
util/file.cc contains a modified implementation of mkstemp under the LGPL. 
jam-files/LICENSE_1_0.txt covers most of that directory (except sanity.jam which is mine).

For the rest:

    KenLM is free software: you can redistribute it and/or modify
    it under the terms of the GNU Lesser General Public License as published
    by the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    KenLM is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public License
    along with Avenue code.  If not, see <http://www.gnu.org/licenses/>.