While theoretically Linux viruses exist, the risk of getting one of them is extremely low so you don't need an antivirus. (Related question: The myths about malware in Unix / Linux)
Disk fragmentation is usually low on Linux filesystems so you don't need any defrag utility.
About tools that blindly perform "disk cleanups", I don't recommend these neither; it's a much better approach understanding what is in your system and get rid of whatever isn't needed (e.g. remove unnecessary services, uninstall unused packages, etc.) For this, a solid understanding of Linux is very important. (Related question: Making the move from Win to Linux)