Hi there, Im the creator of MIDI Goblin. It's an open source, esp32 powered 5 pin midi device that does a whole bunch of things. I posted about it here a while back but I've since made a few improvements. I also made a couple new youtube videos that go into detail on how to use it as a hardware patch librarian and how to use it as an arpeggiator for synths with no internal arpeggiator (as well as midi controllers)

heres the video detailing using it as a patch librarian

<a title="Patch Librarian tutorial - youtube" href=" removed link " target="_blank" rel="noopener">Patch Librarian tutorial - youtube

and heres the video that shows how to use it as an arpeggiator

<a title="Arpeggiator tutorial - youtube" href=" removed link " target="_blank" rel="noopener">Arpeggiator tutorial - youtube

It does a whole lot of other things too, here are the current little "apps" it can run

• hardware patch librarian for user defined devices (midi controllers and synths and even synths with only midi input like volca keys)
• patch morpher
• arpeggiator for received notes (works with synths and midi controllers)
• scale generator (very basic right now)
• chord generator (very basic right now)
• midi cc lfo
• 32 step sequencer
• cc remapper (primative but it works)
• midi controller (for cc parameters, nrpn is in the works)
• monitor for received midi messages (works with nrpn, cc and note messages)

It also has a few other features as well.

• all the apps can run at the same time
• arpeggiator can be synced to the sequencer (scale generator is planned to as well)
• it can use its internal clock or midi clock messages to control the speed of the sequencer or arpeggiator
• it can send program change messages
• 3 user defined buttons that can toggle apps on/off, load patches, load sequences or send panic messages
• all the user defined button actions can also be triggered by up to 99 received midi cc messages
• the output midi channel for each "app" can be set individually
• settings for all apps, triggers, midi channels, user buttons are unique to each synth users add
• files are saved to a removable micro sd card
• theres a wizard for adding devices like synths and midi controllers
• it comes with multiple synths pre-installed

Also its open source. You can get the firmware <a title="firmware" href=" removed link " target="_blank" rel="noopener">here and the schematics are available <a title="schematics" href=" removed link " target="_blank" rel="noopener">here, theres also some available IO on the pcb that could allow tinkerers to add their own mods if they want. Though it's definitely a lot easier to just pre-order one through <a title="pre-order" href=" removed link " target="_blank" rel="noopener">backerkit.com with the info available on <a title="official website" href=" removed link " target="_blank" rel="noopener">midigoblin.com you could make your own goblin for sure. 
MIDI Goblin is a one-man project right now, but I ran a kickstarter for it last year and am currently shipping orders, I'm am pretty happy with how things are going (though I definitely ended up loosing money on the kickstarter campaign (d'oh!))