Estimated tax forms for 2014 are still available at efile.com, as of September 2015. Form 1040-ES and Form 1040-ES (NR), which is to be used for nonresident aliens in the United States, can be downloaded. However, only Form 1040-ES can be filed electronically, as efile.com points out.
Individuals should only file estimated tax forms on income that has no tax withheld from it, as the Internal Revenue Service explains. Earnings from self-employment, interest, rent and alimony are all subject to estimated tax. Taxpayers should also file estimated tax forms if they don't use voluntary withholding on Social Security benefits or unemployment payments.