The 1.0 version of SEQ541 for Mac was available to download on the developer's website when we last checked. We cannot confirm if there is a free download of this app available. The following version: 1.0 is the most frequently downloaded one by the program users.
This free Mac application is a product of Robert Rose. Please check the Mac app with an antivirus before launch as it is downloaded from the developer's website, and we cannot ensure that it is safe. The program lies within Audio & Video Tools, more precisely Music Production.
From the developer:
SEQ541 is a MIDI pattern sequencer for OS X. The program is extremely flexible, all it requires is that you have an external MIDI device generating a clock and it will output notes in time to a pattern sequence you specify.
If you have a hardware (or software) synth that you wish you could control using patterns, this is your program!
You may want to check out more software for Mac, such as Mandala Virtual Brain, Nodal CAD Software or S90 ES Tools, which might be related to SEQ541.