I had been looking for a freeware equivalent of Microsoft Project and came across several project management software which were by and large, pretty impressive. However, I found that OpenProj (from Serena Software) came closest to the "user experience" of MS Project. The layout and functions are almost identical to MS Project, which I had been using for well over 10 years. When I got myself a new laptop, I didn't want to pay the high price of the real deal, but OpenProj fit the bill to a T, and was freeware to boot (excuse the pun!).
I have been using OpenProj for a couple of months and I have not encountered any limitations in terms of numbers of tasks I could input in it so far. The user interface is very close to MS Project and I could use it without being concious of the differences, which says something about the design of the software. All the major function which I normally used such as linking tasks, critical task identification, allocating resources and costs, etc., etc., is all there. Some functions which is seldom used such as having column fields output results based on manipulations of other column informations are not present but is hardly missed if only basic functions are required.
All in all, this is a very well crafted piece of freeware and well worth a go if you are managing small to medium sized projects.