Some brokers allow you a 'free VPS' if you hit certain volumes of trades with them.
Their business model here is they take some of the commissions or spreads that they've earned from you to fund the third party VPS service.
If you're simply asking for a 'free - no strings attached' kind of VPS; which is e.g. Windows based and super easy to set-up; I don't believe these are easy to find at all. If you do, I'd be careful about what they are getting out of it (or you).
Whisquer