Survey of varieties of non-standard analysis? Is there a reliable, reasonably up-to-date, survey article doing a "compare and contrast" on varieties of non-standard analysis?

The best starting point is the detailed account by Hamkins here which will hopefully be published in a more formal venue eventually.

Two approaches that are not discussed there in detail are Hrbacek's _relative set theory_ , as well as the $\alpha$-theory of Di Nasso and collaborators.

Also, the new edition of _Nonstandard analysis for the working mathematician_ by Loeb and Wolff seems promising; see here. However I haven't been able to get my hands on a copy yet.

Such an article is online here, soon to appear in _Real Analysis Exchange_.