So long as there isn't another court that is more specific to your lawsuit (for example, eviction court), then the lawsuit can be filed in small claims.
The most common types of small claims lawsuits in California are:
Security Deposit. Your landlord did not return your security deposit.
Rent. Your tenant or roommate didn't pay the rent.
Loan. You loaned someone money and they didn't pay you back.
Car Accident. Someone hit your car while driving and now you have to pay for the repair work.
Mechanic. You hired a mechanic to repair your car and they did a terrible job.
Contractors. You hired a contractor to perform work at your home and they did a terrible job.
Neighbor. Your neighbor damaged your property.
Contracts. You had a contract with someone and they broke the contract.
Damage to Property. Someone damaged your property (e.g. house, car, bicycle).
Goods. You bought an item and didn't receive it or you sold an item and didn't get paid for it.
Insurance Companies. Your insurance company didn't pay you for a claim they should have paid you for.
Services. You paid for a service and didn't receive it or you provided a service and didn't get paid.
Personal Injury. Someone caused you to get hurt.