Among other things (change logs below), they both sport a new preset browser. I took Diva out for a spin and the preset browser is definitely fleshed out over previous releases, now supporting tags (not user-defined from what I can tell, but the available options look to provide sufficient coverage) as well as color coded favorites. It's not as fully baked as say Omnisphere's browser, but it's a welcome improvement over the previous release.
Diva release notes:
Zebra release notes:New features and improvements:
New Preset Browser
Pitchbend range is now +/−48
New user defined MIDI CC sources replace fixed expression and breath modulation
Mouseover shows parameter values in Data Display
GUI performance improvements on Windows
Plug-in format and OS information shown next to revision number
Improved VST3 implementation
Windows installer now certified
Init preset can be loaded from Data Display
Increased maximum number of skins from 10 to 20
Improved handling of 14bit MIDI CC assignment
Added UTF-8 support for registration names
Bug fixes:
Fixed unsorted folders and presets when using APFS in macOS High Sierra
Fixed possible crash in Cubase when selecting presets (Mac OS X only)
Fixed an issue where the VST3 version did not remember preset name in Data Display (Windows only)
Fixed an issue with Digital oscillator where the multisaw had phase-reset on first notes
Fixed an issue where Finetune parameter could not be locked
Fixed an issue when using the AAX version, the Offline Accuracy was not recognized
Fixed an issue when using the AAX version, saving presets was not possible (Windows only)
Fixed an issue when Transient mode is set to Analog and did not work correctly in mono modes
Fixed an issue where envelopes were sometimes ignoring Attack value
Fixed an issue where long preset names could extend outside the Data Display or Preset Browser window
Various small fixes and improvements
Known issues:
Crash when trying to load script presets (e.g. Randomizer)
New features and improvements:
New Preset Browser
New DotEight and DarkEight skins
Fold wavefolder module added
NuRev reverb module added
Pitchbend range is now +/−48
New user defined MIDI CC sources replace fixed expression and breath modulation
Fullsize editor for OSC, MSEG and MMAP modules
FMO module has waveform previews in new skins
Modulation table for MSEG and MMAP modules
XY controls now have fine control via shift-click
Mouseover shows parameter values in Data Display
GUI performance improvements on Windows
Plug-in format and OS information shown next to revision number
Improved VST3 implementation
Windows installer now certified
Init preset can be loaded from Data Display
Preset organization unified between macOS and Windows
Increased maximum number of skins from 10 to 20
More parameters exposed to host automation
Improved handling of 14bit MIDI CC assignment
Added UTF-8 support for registration names
Bug fixes:
Fixed unsorted folders and presets when using APFS in macOS High Sierra
Fixed possible crash in Cubase when selecting presets (Mac OS X only)
Fixed an issue where VST3 did not remember preset name in Data Display (Windows only)
Fixed an issue where playing very high notes could lead to a crash
Fixed issue where formant filter caused volume spikes when used at 96kHz sample rate
Fixed an issue where Zebrify MSEG was retriggering when in single trigger mode
Fixed an issue where last active arp mod value was used after switching to different play mode
Fixed an issue where the first note of arpeggio sometimes played an additional note
Fixed an issue where long preset names could extend outside the Data Display or Preset Browser window
Various small fixes and improvements
Known issues:
Crash when trying to load script presets (e.g. Randomizer)