Visual Assembler v2.5.2 is a desktop application from RetroBoj that lets you learn and write Commodore 64 machine code programs visually.

It is aimed at anyone who wants to pick up C64 machine code without working blind, since the whole process is done on screen.
Changes:
New: SID Editor previews on the real SID: the instrument Preview, the virtual keyboard, note entry, chord and arpeggio previews, row preview and single-pattern playback now play through the WebSid emulator, streamed frame by frame from the same engine as the exported player. It is preloaded, so notes sound at once.
Note-off in the tracker: key 1 writes === โ the gate is released and the instrument’s release runs, like a key-off in other trackers. Enter edits the selected cell.
Detachable tracker: the tracker can float in its own resizable panel and dock back, so a long wave table leaves it room.
Wave / arpeggio presets: the preset list keeps the chosen preset until the table is edited by hand.
VA-VK: the virtual keyboard has a new name and Play / Stop buttons, and remembers its position and settings; the SID editor remembers its master volume. Knowledge Base: C64 OS development environment and png2c64 links, in two columns.
From 2.5.1: SID Editor instruments like a real tracker (resonant filter sweeps, vibrato, PWM, hard restart, wave / arpeggio tables, RING and SYNC), the new frame-based SID player, Ultimate Basic 1.6.2 tune lines, bookmarks and Go to line.
Source