In general terms Orbit is a family of 29 Go-like games, all of them playable but some more intriguing than others. The version given here as standard was described in Issue 12 of Abstract Games. It also appeared in November 2001 Games, where it was called Half-prohibition Orbit. (The essential rules can be summed up as, "Half-orbits prohibit, orbits capture and prohibit.")
Although stones are captured during the course of the game, Orbit can still be easily played with pen-and-paper. The reason is that captured positions are not subsequently re-occupied --- it is illegal for the captured player to do so, and it is a wasted move for the capturing player to do so. Orbit probably isn't as graceful of a game as Anchor, but if you're the "hardcore" type who likes a maximum challenge, then I think there's a good chance you'll enjoy it.
Addendum: In case anyone's curious, I thought I'd go ahead and briefly describe the full Orbit family. There are 26 "nuts-and-bolts" variants and three special variants. In Orbit there can be up to three kinds of structures: quarter-orbits, half-orbits and orbits. A given structure can function in one of two ways: prohibit, or capture and prohibit. If you take all the permutations of the existence and non-existence of the structures, and cross that with the two function choices, you get 26 variants. The standard game and "quarter-prohibition Orbit" are among these. The first special variant is Conversion Orbit, which I've renamed conversion Go. The second special variant is the "torus" variant: a regular board is used with the understanding that the left and right sides are connected, and the top and bottom sides are connected. There is only one rule: orbits capture and prohibit. (If you decide to try this one out sometime, remember the following important fact: an orbit is only valid if it is inherently self-connected --- a self-connection resulting merely from the toric nature of the playing area is not a sufficient condition.) The third special variant is as follows: half-orbits prohibit, orbits capture and prohibit --- but all outside liberties must be filled. (Inside liberties do not need to be filled.) So in this variant the mechanism of liberties is partially adopted.
As of March 2005, Orbit has been implemented for Richard's by Cameron Browne and is playable with Paul van Wamelen's graphical interface! (Please note that the implementation does not know how to recognize --- and therefore cannot automatically remove --- doomed stones at the end of the game, often resulting in an incorrect final score.)