Synei Backup Manager is a small (1.5MB) and very simple backup tool.
At its core, the program is just about copying the contents of one source folder (including its subfolders) to a destination folder somewhere else. So you can't specify multiple folders, or individual files - it's this one folder only. (Although if that's just not enough, you can create multiple backup jobs and assign a different folder to each.)
If you can live with that issue, though, the rest of the program is surprisingly capable. It allows you to add the date and time to your destination folder names; exclude filters help you ignore specific folders from a backup; you can run the backups in "sync" (copying only new or changed files) or "overwrite" (copying everything) mode; there are options to compress or encrypt your backups, and you even get a simple scheduler.
Synei Backup Manager is clearly never going to replace a full-strength backup tool. If just backing up one or two folders is enough, though, and you need something small and portable, then it could be a good choice. In which case, there's no adware here, no registration required or other hassles, so just download a copy of the program and give it a try.