I helped write an in-house CRM for my current employer as a transition away from Dynamics. It does leads, ownership, billing, conversion, all that stuff and it'

I helped write an in-house CRM for my current employer as a transition away from Dynamics. It does leads, ownership, billing, conversion, all that stuff and it's built as a part of our existing backend systems, which is great for providing extra customer detail and insight you wouldn't get otherwise. It might become a maintenance hassle five or ten years down the track, or after most of the original developers move on, but for now it was simple to write, the best solution to our problems, perfectly customisable to our precise needs and everyone enjoys using it. I used plain excel to maintain a "CRM" of about 200 entries for a university society. Works incredibly well, fast and easy - exactly what you would want in a startup - i suppose until you have multiple people needing to work on it, and come upon data permission and file locking issues. I know several large businesses rely disproportionately on excel in this way.