Other captaining software try to sell themselves as the spreadsheet killer, as if you should be paying extra (as a volunteer captain) to release yourselves fomr the shackles of managing your team on a Google Sheet. I honestly don't think spreadsheets are that bad. League tennis has managed how long without fancy software?
Before you pay for league tennis software, give spreadsheets a try. If you've given spreadsheets a try, maybe try out go-to template. I've been using it for years and have heard my players mention that they love it for the teams they captain as well.
As a captain, I really enjoy having the automatic color-coding of player availability on the lineups sheet. It's also nice to have the number of lines each player is assigned to readily available so I can make sure everyone gets an even number of matches (that's my personal captaining philosophy, yours may be different!)
Check out our template here: USTA Team Spreadsheet
This template is optimized for leagues with the same weekly match time (notably USTA Colorado leagues). You may have to tweak it for leagues with non-regularly-recurring match times!