ShareLaTeX (click here to register a free account) is a wonderful and reliable on-line editor for writing and compiling LaTeX documents “in the cloud” as well as working together in real-time (imagine Google Docs supporting LaTeX => you get ShareLaTeX).

What is even more, the ShareLaTeX team recently announced that now its users are able to prepare documents using knitr!
Note that R version 2.14.1 (2011-12-22) is only available.

Here is an exemplary chunk in an .Rtex file giving the list of installed packages:

%% begin.rcode
% cat(strwrap(paste(sort(rownames(installed.packages())), collapse=", "), 
%    width=80), sep='\n')
%% end.rcode

which results in:

## AER, BayesX, CircStats, CompQuadForm, DAAG, Ecdat, FMStable, Formula, HSAUR,
## KernSmooth, LearnBayes, MASS, MBESS, MCMCpack, MatchIt, Matching, Matrix,
## MatrixModels, PKPDmodels, R2WinBUGS, RANN, RColorBrewer, RUnit, Rcgmin, Rglpk,
## Rvmmin, SimComp, SparseM, TH.data, TSP, WhatIf, Zelig, abind, acepack, ade4,
## ade4TkGUI, adehabitatLT, adehabitatMA, akima, alr3, animation, ape, base,
## bdsmatrix, biclust, bitops, boot, caTools, candisc, car, cba, chron, class,
## clue, cluster, coda, codetools, coin, colorspace, compiler, corrgram, corrplot,
## coxme, cshapes, cubature, datasets, date, deldir, dfoptim, dichromat, digest,
## diveMove, doMC, dynlm, e1071, effects, ellipse, evaluate, expm, fBasics,
## flexclust, foreach, foreign, formatR, fts, gWidgets, gam, gbm, gclus, gdata,
## gee, geosphere, ggplot2, gpclib, grDevices, graphics, grid, gss, gstat, gtable,
## gtools, heplots, hexbin, highr, igraph, igraphdata, ineq, intervals, ipred,
## isa2, iterators, itertools, kernlab, knitr, labeling, lattice, latticeExtra,
## leaps, lmtest, locfit, logspline, lokern, lpSolve, mapdata, mapproj, maps,
## maptools, markdown, matrixcalc, mboost, methods, mgcv, mice, miscTools,
## mitools, mlbench, mnormt, modeltools, mratios, multcomp, munsell, mvtnorm,
## nlme, nnet, nor1mix, np, numDeriv, nws, optextras, optimx, oz, pan, parallel,
## party, pbivnorm, pcaPP, pixmap, plm, plyr, poLCA, polspline, polycor, polynom,
## prodlim, proto, proxy, pscl, quantreg, randomForest, rbounds, relations,
## reshape, reshape2, rlecuyer, rmeta, rpart, sandwich, scales, scatterplot3d,
## sem, seriation, setRNG, sets, sfsmisc, shapefiles, slam, snow, sp, spacetime,
## spatial, spdep, splancs, splines, stabledist, statmod, stats, stats4, stringr,
## strucchange, survey, survival, survival, svGUI, svUnit, systemfit, tcltk,
## testit, testthat, timeDate, timeSeries, tis, tools, tripack, tweedie, ucminf,
## urca, utils, vcd, waveslim, xtable, xts, zoo

Installation of new packages has been disabled (as well as any access to on-line resources). However, you may upload your data sets (e.g. in CSV format) to your projects and read them with R commands. It seems that the compilation takes place in a chrooted-like environment, so it is secure.

Enjoy!