Export Excel files with multiple sheets from R using XLSX

require(xlsx)
wb = createWorkbook()

# Create a first sheet
sheet  = createSheet(wb, sheetName="NewSheet.1")
rows = createRow(sheet, rowIndex=1:2)
cells = createCell(rows, colIndex=1:8)
setCellValue(cells[[1,1]],"Text")
setCellValue(cells[[1,2]],-0.1)
setCellValue(cells[[1,3]],"=B1+1")

# Create another sheet
sheet  = createSheet(wb, sheetName="NewSheet.2")
rows = createRow(sheet, rowIndex=1:2)
cells = createCell(rows, colIndex=1:8)
setCellValue(cells[[1,1]],"Text")

# Save Excel file and show me the names of the sheets that have been created
saveWorkbook(wb, "trying out.xlsx")
names(getSheets(wb) )

XLSX Package on CRAN

XLSX is based on the Apache  POI project. I still need to figure out  how to evaluate formulas in the Excel file. There may be some help at the Apache POI formula evaluation page.