Playbeat is a deep program that, despite the smooth aesthetic, currently suffers from interface overload. In my day I spent a good amount of time on HCI, so please take these suggestions as coming from a trusted source.
The most important improvement would be to add context mouse tooltips. Not every icon is clear, especially at small sizes. This would also allow the removal of certain text (e.g. Mixer, Export) saving space. (I have read that this feature was promised some time ago. Please make it a priority, as it will allow users a much nicer learning experience, cut down on tech support, etc.)
Export can be moved to the top panel, next to MIDI Learn and Setup. Also move the Mixer and Remix/trigger icons. All of these functions have one thing in common: they replace the sequencer completely. For clarity, only icons on the top bar should do this (exception: sample edit).
The Disintegration mode icon should be integrated with the Infinity icon, so the related functionality is obvious.
The clear all (reset) icon should be moved up with undo/redo, so that functionality is grouped and it’s less likely to be hit accidentally. And IMO this function should have a confirmation dialogue.
The main panel effectively has six “tabs” (steps, density, pitch, flam, volume, and pan) which change the line of icons just below them (which I will call the tab menu) and also change the sequencer interface. But the tab menu is not distinct and the tabs do not look like tabs. These should be restyled to make this relationship obvious. UI space can be saved as a result. For example, it’s unnecesary for each tab label to have a randomise button. Just add one randomise icon on the tab menu. (And please make the die icon identical everywhere there is a random function.)
The icons for changing sequencer steps are very small and cluttered (on all tabs except for the Steps tab itself) due to the plethora of little arrows. Remove these arrows so that the values themselves can be larger and easier to interact with. It’s obvious enough that a click’n’drag will change the values (especially with tooltips, ahem). Also, a double click should return a value to its default (pan to centre, etc.).
Allow changing skins to suit people with different visual ability. This would include font sizes (to the degree that is possible).
Allow custom naming of tracks. A few alphanumeric characters might be enough of a scribble space.
This got a bit long. I should get back to making music! I hope the suggestions are helpful.