Have you ever walked into a house and had an indescribable feeling that it just feels cheap? A professional builder would walk in and give you a laundry list of shortcomings: uneven drywall, gappy hardwood floors, hollow-core doors, and cheap hardware. But most people just have a gut reaction. Like a well-built home, great software focuses on giving its users hundreds of small, satisfying interactions. A great transition in a mobile app gives us the same feeling we get from using a well-made door handle on a solid oak door — you may not be able to put your finger on it, but man, does the house ever feel well built. Slack is really fun to use. It feels like a well-built house.