Review of Miranda powered by the Slant community.
Miranda is free and open-source
Ranked in these QuestionsQuestion Ranking
Pros
Pro Requires no installation and is very lightweight
Very light on system resources and extremely fast, Miranda IM requires no installation and can be made to fit on a single floppy disk or USB drive.
Pro Insanely customisable
You can see all the plugins available for Miranda here.
Cons
Con Outdated XMPP Support
Missing OMEMO, Carbon Copy, HTTP-Upload ...