South Africa international captain Khumalo, 26, featured in last week's friendly against Bradford, partnering
Khumalo joined Spurs from Supersport United in 2010 and has also enjoyed loan spells with Preston and Reading.
"I'm very pleased to be here. I'm very happy that things have worked out and I'm just looking forward to the start of the season," he told the club's official website.
"All the lads have been really welcoming, which really helps. I've had a lot of support from the skipper and everyone has made it really easy to make the transition.
"Dean [Furman]and I have met before having played in the national team, so it was great to come here and see a familiar face."
Rovers have been in talks with 22-year-old Forrester for several weeks and compensation is yet to be agreed with the Bees due to his age.
However, the former Aston Villa man has expressed his delight at finally pushing his move to South Yorkshire through.
"I'm very excited to be here, I've been here a while now and have got to know the lads and the manager and I'm really excited for the season ahead," he told the club's official website.
"As soon as I met Paul [Dickov] and John [Ryan] it became a no brainier for me; I spoke to my agent straight away and told him I thought Doncaster is the place for me.
"The deal was done a couple of days after that and now I'm just really happy to get things going.
"There's a good core to the team here, we will have to add a couple of new faces which I'm sure the backroom staff are looking at now.
"The team and players that we have got here at the moment are good enough but with further additions we can give it a real go - it's not going to be easy but we have got to enjoy it."
Doncaster made their third signing of the day with the capture of Turnbull.
The 28-year-old, who is a former England youth international, has penned a one-year deal at the Keepmoat following his release from Premier League Chelsea earlier this summer.
The goalkeeping position was an area that urgently needed attending to by Dickov as after the release of Gary Woods and Neil Sullivan over the summer, they only had rookie keeper Jonathan Maxted on their books.
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