A WBS maker with a Gantt timeline.
Break the project down, the schedule builds itself.

A project taken apart from the general to the specific, level by level, until the bottom of the tree is a list of individual tasks somebody can pick up, size and finish. Estimate those tasks and every level above them adds itself up. The long answer - the 100% rule, sizing in t-shirts or man-days, a worked example - is in our guide: What is a work breakdown structure?

Break the work down first, then estimate only the leaves. An estimate made on a whole initiative is a guess, because nobody can hold it in their head at once, while an estimate made on forty small tasks is arithmetic over forty judgements you can argue with one at a time. Size the leaves in t-shirt sizes while the scope is still moving and in man-days once it has settled, and put contingency where the uncertainty actually sits rather than as one padded number at the end. Every level above the leaves then adds itself up, so the total cannot quietly disagree with the tasks underneath it.

Start from the estimate, not from the date somebody wants. Put the sized tasks in the order they can actually be done, count in working days so that weekends do not silently vanish from the plan, and let each parent take its dates from the children below it instead of being typed in by hand. A schedule is realistic exactly when every date on it is derived from work that someone has sized. Compare that result with the date you were hoping for, and when the two disagree, change the scope or the people - changing the arithmetic only moves the surprise later.

It depends on which part of Microsoft Project you actually use. For a sized breakdown and a timeline, in a browser, with nothing to install, TreeProjectPlan does that and deliberately nothing else. For task dependencies, resources and baselines on one machine, GanttProject and ProjectLibre are free, open source and much closer to Microsoft Project in shape. For a team that has to work in one plan at once, OpenProject Community Edition is free to license, but somebody has to host it. Microsoft Project itself is not free, and nothing free replaces its resource leveling and portfolio reporting: the full comparison is in the shortlist above.

Yes, and for a small tree it is the right answer: you already have one, everybody can open it, and nothing has to be learned. The limit is that indentation in a spreadsheet is decoration - the sheet does not know that a row is a child of the row above it - so every rollup, every working-day count and every bar of a chart is a formula you write and then maintain by hand. That holds for twenty tasks and stops holding somewhere around the fourth level of the tree.

In your browser, under a single key in local storage. That is the only copy unless you sign in and save one to your account, and nothing is uploaded until you ask for it. Clearing browser data, a private window or a different machine means it is not there - export anything that matters.

No. TreeProjectPlan needs no account and no sign-up: open the page and start typing. Your plan is saved in your own browser, and you can export it to a file whenever you want a copy.

Yes. It is static files - once the page is open it keeps working with the network off, and it can be opened straight from disk.

Several thousand rows. Only the rows near the viewport are drawn, in both the table and the chart, so scrolling stays smooth as the tree grows.

Nothing, for a single user: the whole editor is free with no account to create, and no feature sits behind a paywall. A paid license adds one thing, which is your plans saved to your account instead of only in one browser, and nothing is ever charged without your explicit agreement. The prices are on the pricing page and the Terms of Use say what a license covers.