Bootloader Mode is launched by pressing and holding the "m" button (Mode button) while switching on Osmose. It can be used to make OsmoseUpdater detect Osmose as "connected" when it isn't recognized when booting normally, also see My Osmose is bricked and only shows a blank screen. When using Bootloader Mode, the screen will remain blank, with only the backlight turned on. Bootloader Mode allows only the separate flashing of the Osmose operating system. Backup/Restore actions or flashing the DSP firmware isn't possible in this mode, because they require access to the DSP.
Safe Mode is launched by pressing and holding the first menu button (the one usually opening presets menu) while switching on Osmose. Several functions won't be accessible when launching in Safe Mode, but this mode is helpful to skip loading flash memory in case this memory gets corrupted somehow. Also see My Osmose is stuck during booting and keeps on restarting.
Haken Recovery Mode is launched by pressing and holding the fourth menu button (the one below the master volume knob) while switching on Osmose.
This Mode is not expected to be needed by the user. It loads an old version of the Haken DSP firmware to verify whether the DSP card (Haken Board) responds at all. An example of troubleshooting would be if the info tab in Osmose's global settings and the OsmoseUpdater don't show any haken version / dsp version when booting normally. If booting in Haken Recovery Mode makes an old haken version / dsp version appear in info tab and in OsmoseUpdater, then it means that a basic connection to the Haken DSP board can be established and further troubleshooting like a DSP flash might be fruitful.