Guyatone's Micro Series pedals are awesome, they were doing the 'small footprint' thing before just about anyone else. Back in the 80s, Boss did a pedal called a 'Slow Gear', with an automated swell-in attack designed to emulate a violin. They cost heeeeeeaps now and haven't been reissued, but now and again other companies have a crack at the same idea. This one has a bit more scope in the controls than others I've tried, so you can dial in longer swell-in and the threshold control is very responsive. Plus, it's tiny and adorably purple.  

Model: Guyatone SV2 Slow Volume 
Made: Japan, mid 90s approx (serial 25021585)
Type: auto-swell
Power: standard 9v supply or battery
Switching: true bypass
Equivalent new street price (approx): n/a (discontinued)
Mods: none
Accessories: no box or manual
Condition notes: used, few minor marks, very good condition