Anything that doesn't fit into other topics goes here!
Is it possible to make a glissando in LMMS, a continuous glide from one pitch to another ?

Yes, .. and no :D

The LB 302 has a flag to set glide on.
All Plugins have a pitch-correction, but it has not a wide range.
When you want to slide with the 3xOSC you can automize the basepoint (note) by dragging it into an automation track. But this isn't a really sliding, it is just a 'walking' though the notes.

I think sliding is a part of the plugin you're using. Try an LFO on the pitch of the synth (VSTI?). So you have less artefacts, too.

-yes, and as from 0.4.8 zynAddSubFX has a knob for portamento on the GUI, meaning that you can use automation also. It is only posible to set it 'on/off' even though the knob 'spans' 0..127 it unfortunately does not indicate 'time of event'. >64 in 'on'