Surge is an awesome open source synthesizer that is getting updated all the time: https://github.com/surge-synthesizer/surge

LMMS is a digital audio workstation, not a synth. If you're looking for another FOSS DAW there is Ardour.

Is the creator going to release updates on the github repository or is this the last version that's released as open source? Because the github seems to be out of date a bit.