MBROLA is speech synthesis software as a worldwide collaborative project. It started in 1995 at the TCTS Lab of the Faculté polytechnique de Mons (Belgium) as a scientific project to obtain a set of speech synthesizers for as many languages as possible. Back than it was non-free software, but on October 24, 2018, source code was released on GitHub under the GNU Affero General Public License. On January 23, 2019, a tool called MBROLATOR was released to provide creation of MBROLA database from WAV files with the same license.
Now there are multiple synth compatible with MBROLA including SEKAI. SEKAI also includes a tool to build MBROLA speech databases and MBROLAsing UTAU voices (for singing synthesis).