Question: I am looking for a visual tail tool that can monitor several local or remote log files.

Optional features that interest me: color highlight based on log error level, coloring for special words, filtering of messages and/or notifications on new activity.

Answer: 
You may try to use a combination of `multitail` and `ssh`.

* <https://serverfault.com/questions/53976/use-local-tools-to-monitor-remote-logs>
* <https://superuser.com/questions/320575/mac-os-x-logfile-viewer>
Might I suggest the [LogTail macOS app](https://itunes.apple.com/us/app/logtail/id1073404370?ls=1&mt=12) - it checks all the requirements you mentioned (except the notifications part). It has SSH based remote log viewing functionality and can tail the remote log file (configurable polling interval). You can setup multiple SSH servers and browse them to select the log file to view.

It supports filtering and/or highlighting search patterns, searching the remote log file incrementally, and lets you adjust the foreground, background colors and font.

Also, it doesn't load the entire remote log file at once but intelligently fetches content based on your scrolling actions, so it is quite efficient.

The app [site](http://www.logtailapp.com/) has more information. Hope it helps! 

PS: I'm the app developer :)