Entertainment Partners (Movie Magic’s EP Scheduling), Gorilla Film Productions Software, No Budget Filmmaking Ultrapack, Showbiz Budgeting and Final Draft are all by their own merits reliable preproduction, production and post production software that will assist you in the organizational process of filmmaking at any budget. Some are easier than others to learn but all the above mentioned software cost money.
At the time of this writing, Celtx is a free complete film production software.
As it is common by each manufacturer’s own approach to the film production workflow some of the features you will find on other software may not be found on Celtx and vice versa. But of course Celtx is a free shareware.