Ownable.sol

// SPDX-License-Identifier: GPL-3.0

pragma solidity ^0.8.0;

contract OwnedContract {
    address public owner;

    constructor() {
        owner = msg.sender;
    }

    modifier onlyOwner() {
        require(msg.sender == owner, "Only the contract owner can call this function.");
        _;
    }

    function transferOwnership(address newOwner) external onlyOwner {
        require(newOwner != address(0), "Invalid address.");
        owner = newOwner;
    }
    
    // Example function only callable by the contract owner
    function doSomething() external onlyOwner {
        // Perform some privileged operation
    }
}