Ask HN: Where to find beta testers for an OSX app?

For a new app that I'm building, I've decided to embrace the Lean Startup approach, and give out lots of beta copies in exchange for feedback and bug reports.

My question is where's a good place to get a around 15-20 beta testers to play with my app? There seem to be such services for mobile apps, but I can't seem to find a place to test out my desktop app.

P.S: In any case, if you want to play with the app (it's a very simple productivity app), leave me your email or contact me via my profile.