Basecamp

Basecamp takes an opinionated, minimalist approach: to-dos, message boards, docs, schedules and group chat, and not much else. There are no boards, no Gantt charts, no custom fields — a deliberate choice by 37signals (the company behind it) to reduce tool sprawl and busywork.

Pricing is flat-rate per organization rather than per seat, which makes it unusually predictable for larger teams, though it can be relatively pricier for very small ones.