I went through two rounds, each with the CEO, Rick Hou, and two engineers. Both rounds were very positive. Final round seemed to go great, and at the end Rick said that the next step would be talking to HR for salary and compensation, so obviously things were looking hopeful. That was 6 weeks ago, and they've been radio silent. I followed up 3 times with Rick and with the engineers. It's too bad that they tout their great culture and treat candidates this way. If you're passing on a candidate, simply inform them so. "Ghosting" candidates is extremely unprofessional and lacking in common courtesy.